Replace the BaseFontLoader classes with one FontLoader class

By having just *one* class, and using pre-processor blocks directly in the relevant methods, we reduce the size of this code in the *built* `pdf.js` file.
Originally, when the `BaseFontLoader` abstraction was added in PR 9982, the idea was probably that additional build-targets would get their own implementations. Given that this hasn't happened in the four years since that landed, it doesn't seem meaningful to keep it around.

src/display/font_loader.js

@@ -19,22 +19,17 @@ import {
   FeatureTest,
   shadow,
   string32,
-  unreachable,
   UNSUPPORTED_FEATURES,
   warn,
 } from "../shared/util.js";
 
-class BaseFontLoader {
+class FontLoader {
   constructor({
     docId,
     onUnsupportedFeature,
     ownerDocument = globalThis.document,
-    // For testing only.
+    styleElement = null, // For testing only.
-    styleElement = null,
   }) {
-    if (this.constructor === BaseFontLoader) {
-      unreachable("Cannot initialize BaseFontLoader.");
-    }
     this.docId = docId;
     this._onUnsupportedFeature = onUnsupportedFeature;
     this._document = ownerDocument;
@@ -44,6 +39,11 @@ class BaseFontLoader {
       typeof PDFJSDev === "undefined" || PDFJSDev.test("!PRODUCTION || TESTING")
         ? styleElement
         : null;
+
+    if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("MOZCENTRAL")) {
+      this.loadingRequests = [];
+      this.loadTestFontId = 0;
+    }
   }
 
   addNativeFontFace(nativeFontFace) {
@@ -120,10 +120,6 @@ class BaseFontLoader {
     }
   }
 
-  _queueLoadingCallback(callback) {
-    unreachable("Abstract method `_queueLoadingCallback`.");
-  }
-
   get isFontLoadingAPISupported() {
     const hasFonts = !!this._document?.fonts;
     if (
@@ -139,220 +135,198 @@ class BaseFontLoader {
     return shadow(this, "isFontLoadingAPISupported", hasFonts);
   }
 
-  // eslint-disable-next-line getter-return
   get isSyncFontLoadingSupported() {
-    unreachable("Abstract method `isSyncFontLoadingSupported`.");
+    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
-  }
-
-  // eslint-disable-next-line getter-return
-  get _loadTestFont() {
-    unreachable("Abstract method `_loadTestFont`.");
-  }
-
-  _prepareFontLoadEvent(rules, fontsToLoad, request) {
-    unreachable("Abstract method `_prepareFontLoadEvent`.");
-  }
-}
-
-let FontLoader;
-if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
-  FontLoader = class MozcentralFontLoader extends BaseFontLoader {
-    get isSyncFontLoadingSupported() {
       return shadow(this, "isSyncFontLoadingSupported", true);
     }
-  };
-} else {
-  // PDFJSDev.test('CHROME || GENERIC')
 
-  FontLoader = class GenericFontLoader extends BaseFontLoader {
+    let supported = false;
-    constructor(params) {
+    if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("CHROME")) {
-      super(params);
+      if (typeof navigator === "undefined") {
-      this.loadingRequests = [];
+        // Node.js - we can pretend that sync font loading is supported.
-      this.loadTestFontId = 0;
+        supported = true;
-    }
+      } else {
-
+        // User agent string sniffing is bad, but there is no reliable way to
-    get isSyncFontLoadingSupported() {
+        // tell if the font is fully loaded and ready to be used with canvas.
-      let supported = false;
+        const m = /Mozilla\/5.0.*?rv:(\d+).*? Gecko/.exec(navigator.userAgent);
-      if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("CHROME")) {
+        if (m?.[1] >= 14) {
-        if (typeof navigator === "undefined") {
-          // Node.js - we can pretend that sync font loading is supported.
           supported = true;
-        } else {
-          // User agent string sniffing is bad, but there is no reliable way to
-          // tell if the font is fully loaded and ready to be used with canvas.
-          const m = /Mozilla\/5.0.*?rv:(\d+).*? Gecko/.exec(
-            navigator.userAgent
-          );
-          if (m?.[1] >= 14) {
-            supported = true;
-          }
-          // TODO - other browsers...
         }
+        // TODO - other browsers...
       }
-      return shadow(this, "isSyncFontLoadingSupported", supported);
+    }
+    return shadow(this, "isSyncFontLoadingSupported", supported);
+  }
+
+  _queueLoadingCallback(callback) {
+    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
+      throw new Error("Not implemented: _queueLoadingCallback");
     }
 
-    _queueLoadingCallback(callback) {
+    function completeRequest() {
-      function completeRequest() {
+      assert(!request.done, "completeRequest() cannot be called twice.");
-        assert(!request.done, "completeRequest() cannot be called twice.");
+      request.done = true;
-        request.done = true;
 
-        // Sending all completed requests in order of how they were queued.
+      // Sending all completed requests in order of how they were queued.
-        while (loadingRequests.length > 0 && loadingRequests[0].done) {
+      while (loadingRequests.length > 0 && loadingRequests[0].done) {
-          const otherRequest = loadingRequests.shift();
+        const otherRequest = loadingRequests.shift();
-          setTimeout(otherRequest.callback, 0);
+        setTimeout(otherRequest.callback, 0);
-        }
       }
-
-      const { loadingRequests } = this;
-      const request = {
-        done: false,
-        complete: completeRequest,
-        callback,
-      };
-      loadingRequests.push(request);
-      return request;
     }
 
-    get _loadTestFont() {
+    const { loadingRequests } = this;
-      const getLoadTestFont = function () {
+    const request = {
-        // This is a CFF font with 1 glyph for '.' that fills its entire width
+      done: false,
-        // and height.
+      complete: completeRequest,
-        return atob(
+      callback,
-          "T1RUTwALAIAAAwAwQ0ZGIDHtZg4AAAOYAAAAgUZGVE1lkzZwAAAEHAAAABxHREVGABQA" +
+    };
-            "FQAABDgAAAAeT1MvMlYNYwkAAAEgAAAAYGNtYXABDQLUAAACNAAAAUJoZWFk/xVFDQAA" +
+    loadingRequests.push(request);
-            "ALwAAAA2aGhlYQdkA+oAAAD0AAAAJGhtdHgD6AAAAAAEWAAAAAZtYXhwAAJQAAAAARgA" +
+    return request;
-            "AAAGbmFtZVjmdH4AAAGAAAAAsXBvc3T/hgAzAAADeAAAACAAAQAAAAEAALZRFsRfDzz1" +
+  }
-            "AAsD6AAAAADOBOTLAAAAAM4KHDwAAAAAA+gDIQAAAAgAAgAAAAAAAAABAAADIQAAAFoD" +
+
-            "6AAAAAAD6AABAAAAAAAAAAAAAAAAAAAAAQAAUAAAAgAAAAQD6AH0AAUAAAKKArwAAACM" +
+  get _loadTestFont() {
-            "AooCvAAAAeAAMQECAAACAAYJAAAAAAAAAAAAAQAAAAAAAAAAAAAAAFBmRWQAwAAuAC4D" +
+    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
-            "IP84AFoDIQAAAAAAAQAAAAAAAAAAACAAIAABAAAADgCuAAEAAAAAAAAAAQAAAAEAAAAA" +
+      throw new Error("Not implemented: _loadTestFont");
-            "AAEAAQAAAAEAAAAAAAIAAQAAAAEAAAAAAAMAAQAAAAEAAAAAAAQAAQAAAAEAAAAAAAUA" +
-            "AQAAAAEAAAAAAAYAAQAAAAMAAQQJAAAAAgABAAMAAQQJAAEAAgABAAMAAQQJAAIAAgAB" +
-            "AAMAAQQJAAMAAgABAAMAAQQJAAQAAgABAAMAAQQJAAUAAgABAAMAAQQJAAYAAgABWABY" +
-            "AAAAAAAAAwAAAAMAAAAcAAEAAAAAADwAAwABAAAAHAAEACAAAAAEAAQAAQAAAC7//wAA" +
-            "AC7////TAAEAAAAAAAABBgAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
-            "AAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
-            "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
-            "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
-            "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
-            "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAMAAAAAAAD/gwAyAAAAAQAAAAAAAAAAAAAAAAAA" +
-            "AAABAAQEAAEBAQJYAAEBASH4DwD4GwHEAvgcA/gXBIwMAYuL+nz5tQXkD5j3CBLnEQAC" +
-            "AQEBIVhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYAAABAQAADwACAQEEE/t3" +
-            "Dov6fAH6fAT+fPp8+nwHDosMCvm1Cvm1DAz6fBQAAAAAAAABAAAAAMmJbzEAAAAAzgTj" +
-            "FQAAAADOBOQpAAEAAAAAAAAADAAUAAQAAAABAAAAAgABAAAAAAAAAAAD6AAAAAAAAA=="
-        );
-      };
-      return shadow(this, "_loadTestFont", getLoadTestFont());
     }
 
-    _prepareFontLoadEvent(rules, fonts, request) {
+    // This is a CFF font with 1 glyph for '.' that fills its entire width
-      /** Hack begin */
+    // and height.
-      // There's currently no event when a font has finished downloading so the
+    const testFont = atob(
-      // following code is a dirty hack to 'guess' when a font is ready.
+      "T1RUTwALAIAAAwAwQ0ZGIDHtZg4AAAOYAAAAgUZGVE1lkzZwAAAEHAAAABxHREVGABQA" +
-      // It's assumed fonts are loaded in order, so add a known test font after
+        "FQAABDgAAAAeT1MvMlYNYwkAAAEgAAAAYGNtYXABDQLUAAACNAAAAUJoZWFk/xVFDQAA" +
-      // the desired fonts and then test for the loading of that test font.
+        "ALwAAAA2aGhlYQdkA+oAAAD0AAAAJGhtdHgD6AAAAAAEWAAAAAZtYXhwAAJQAAAAARgA" +
+        "AAAGbmFtZVjmdH4AAAGAAAAAsXBvc3T/hgAzAAADeAAAACAAAQAAAAEAALZRFsRfDzz1" +
+        "AAsD6AAAAADOBOTLAAAAAM4KHDwAAAAAA+gDIQAAAAgAAgAAAAAAAAABAAADIQAAAFoD" +
+        "6AAAAAAD6AABAAAAAAAAAAAAAAAAAAAAAQAAUAAAAgAAAAQD6AH0AAUAAAKKArwAAACM" +
+        "AooCvAAAAeAAMQECAAACAAYJAAAAAAAAAAAAAQAAAAAAAAAAAAAAAFBmRWQAwAAuAC4D" +
+        "IP84AFoDIQAAAAAAAQAAAAAAAAAAACAAIAABAAAADgCuAAEAAAAAAAAAAQAAAAEAAAAA" +
+        "AAEAAQAAAAEAAAAAAAIAAQAAAAEAAAAAAAMAAQAAAAEAAAAAAAQAAQAAAAEAAAAAAAUA" +
+        "AQAAAAEAAAAAAAYAAQAAAAMAAQQJAAAAAgABAAMAAQQJAAEAAgABAAMAAQQJAAIAAgAB" +
+        "AAMAAQQJAAMAAgABAAMAAQQJAAQAAgABAAMAAQQJAAUAAgABAAMAAQQJAAYAAgABWABY" +
+        "AAAAAAAAAwAAAAMAAAAcAAEAAAAAADwAAwABAAAAHAAEACAAAAAEAAQAAQAAAC7//wAA" +
+        "AC7////TAAEAAAAAAAABBgAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
+        "AAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
+        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
+        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
+        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
+        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAMAAAAAAAD/gwAyAAAAAQAAAAAAAAAAAAAAAAAA" +
+        "AAABAAQEAAEBAQJYAAEBASH4DwD4GwHEAvgcA/gXBIwMAYuL+nz5tQXkD5j3CBLnEQAC" +
+        "AQEBIVhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYAAABAQAADwACAQEEE/t3" +
+        "Dov6fAH6fAT+fPp8+nwHDosMCvm1Cvm1DAz6fBQAAAAAAAABAAAAAMmJbzEAAAAAzgTj" +
+        "FQAAAADOBOQpAAEAAAAAAAAADAAUAAQAAAABAAAAAgABAAAAAAAAAAAD6AAAAAAAAA=="
+    );
+    return shadow(this, "_loadTestFont", testFont);
+  }
 
-      function int32(data, offset) {
+  _prepareFontLoadEvent(rules, fonts, request) {
-        return (
+    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
-          (data.charCodeAt(offset) << 24) |
+      throw new Error("Not implemented: _prepareFontLoadEvent");
-          (data.charCodeAt(offset + 1) << 16) |
+    }
-          (data.charCodeAt(offset + 2) << 8) |
-          (data.charCodeAt(offset + 3) & 0xff)
-        );
-      }
-      function spliceString(s, offset, remove, insert) {
-        const chunk1 = s.substring(0, offset);
-        const chunk2 = s.substring(offset + remove);
-        return chunk1 + insert + chunk2;
-      }
-      let i, ii;
 
-      // The temporary canvas is used to determine if fonts are loaded.
+    /** Hack begin */
-      const canvas = this._document.createElement("canvas");
+    // There's currently no event when a font has finished downloading so the
-      canvas.width = 1;
+    // following code is a dirty hack to 'guess' when a font is ready.
-      canvas.height = 1;
+    // It's assumed fonts are loaded in order, so add a known test font after
-      const ctx = canvas.getContext("2d");
+    // the desired fonts and then test for the loading of that test font.
 
-      let called = 0;
+    function int32(data, offset) {
-      function isFontReady(name, callback) {
+      return (
-        called++;
+        (data.charCodeAt(offset) << 24) |
-        // With setTimeout clamping this gives the font ~100ms to load.
+        (data.charCodeAt(offset + 1) << 16) |
-        if (called > 30) {
+        (data.charCodeAt(offset + 2) << 8) |
-          warn("Load test font never loaded.");
+        (data.charCodeAt(offset + 3) & 0xff)
-          callback();
-          return;
-        }
-        ctx.font = "30px " + name;
-        ctx.fillText(".", 0, 20);
-        const imageData = ctx.getImageData(0, 0, 1, 1);
-        if (imageData.data[3] > 0) {
-          callback();
-          return;
-        }
-        setTimeout(isFontReady.bind(null, name, callback));
-      }
-
-      const loadTestFontId = `lt${Date.now()}${this.loadTestFontId++}`;
-      // Chromium seems to cache fonts based on a hash of the actual font data,
-      // so the font must be modified for each load test else it will appear to
-      // be loaded already.
-      // TODO: This could maybe be made faster by avoiding the btoa of the full
-      // font by splitting it in chunks before hand and padding the font id.
-      let data = this._loadTestFont;
-      const COMMENT_OFFSET = 976; // has to be on 4 byte boundary (for checksum)
-      data = spliceString(
-        data,
-        COMMENT_OFFSET,
-        loadTestFontId.length,
-        loadTestFontId
       );
-      // CFF checksum is important for IE, adjusting it
-      const CFF_CHECKSUM_OFFSET = 16;
-      const XXXX_VALUE = 0x58585858; // the "comment" filled with 'X'
-      let checksum = int32(data, CFF_CHECKSUM_OFFSET);
-      for (i = 0, ii = loadTestFontId.length - 3; i < ii; i += 4) {
-        checksum = (checksum - XXXX_VALUE + int32(loadTestFontId, i)) | 0;
-      }
-      if (i < loadTestFontId.length) {
-        // align to 4 bytes boundary
-        checksum =
-          (checksum - XXXX_VALUE + int32(loadTestFontId + "XXX", i)) | 0;
-      }
-      data = spliceString(data, CFF_CHECKSUM_OFFSET, 4, string32(checksum));
-
-      const url = `url(data:font/opentype;base64,${btoa(data)});`;
-      const rule = `@font-face {font-family:"${loadTestFontId}";src:${url}}`;
-      this.insertRule(rule);
-
-      const names = [];
-      for (const font of fonts) {
-        names.push(font.loadedName);
-      }
-      names.push(loadTestFontId);
-
-      const div = this._document.createElement("div");
-      div.style.visibility = "hidden";
-      div.style.width = div.style.height = "10px";
-      div.style.position = "absolute";
-      div.style.top = div.style.left = "0px";
-
-      for (const name of names) {
-        const span = this._document.createElement("span");
-        span.textContent = "Hi";
-        span.style.fontFamily = name;
-        div.append(span);
-      }
-      this._document.body.append(div);
-
-      isFontReady(loadTestFontId, () => {
-        div.remove();
-        request.complete();
-      });
-      /** Hack end */
     }
-  };
+    function spliceString(s, offset, remove, insert) {
-} // End of PDFJSDev.test('CHROME || GENERIC')
+      const chunk1 = s.substring(0, offset);
+      const chunk2 = s.substring(offset + remove);
+      return chunk1 + insert + chunk2;
+    }
+    let i, ii;
+
+    // The temporary canvas is used to determine if fonts are loaded.
+    const canvas = this._document.createElement("canvas");
+    canvas.width = 1;
+    canvas.height = 1;
+    const ctx = canvas.getContext("2d");
+
+    let called = 0;
+    function isFontReady(name, callback) {
+      called++;
+      // With setTimeout clamping this gives the font ~100ms to load.
+      if (called > 30) {
+        warn("Load test font never loaded.");
+        callback();
+        return;
+      }
+      ctx.font = "30px " + name;
+      ctx.fillText(".", 0, 20);
+      const imageData = ctx.getImageData(0, 0, 1, 1);
+      if (imageData.data[3] > 0) {
+        callback();
+        return;
+      }
+      setTimeout(isFontReady.bind(null, name, callback));
+    }
+
+    const loadTestFontId = `lt${Date.now()}${this.loadTestFontId++}`;
+    // Chromium seems to cache fonts based on a hash of the actual font data,
+    // so the font must be modified for each load test else it will appear to
+    // be loaded already.
+    // TODO: This could maybe be made faster by avoiding the btoa of the full
+    // font by splitting it in chunks before hand and padding the font id.
+    let data = this._loadTestFont;
+    const COMMENT_OFFSET = 976; // has to be on 4 byte boundary (for checksum)
+    data = spliceString(
+      data,
+      COMMENT_OFFSET,
+      loadTestFontId.length,
+      loadTestFontId
+    );
+    // CFF checksum is important for IE, adjusting it
+    const CFF_CHECKSUM_OFFSET = 16;
+    const XXXX_VALUE = 0x58585858; // the "comment" filled with 'X'
+    let checksum = int32(data, CFF_CHECKSUM_OFFSET);
+    for (i = 0, ii = loadTestFontId.length - 3; i < ii; i += 4) {
+      checksum = (checksum - XXXX_VALUE + int32(loadTestFontId, i)) | 0;
+    }
+    if (i < loadTestFontId.length) {
+      // align to 4 bytes boundary
+      checksum = (checksum - XXXX_VALUE + int32(loadTestFontId + "XXX", i)) | 0;
+    }
+    data = spliceString(data, CFF_CHECKSUM_OFFSET, 4, string32(checksum));
+
+    const url = `url(data:font/opentype;base64,${btoa(data)});`;
+    const rule = `@font-face {font-family:"${loadTestFontId}";src:${url}}`;
+    this.insertRule(rule);
+
+    const names = [];
+    for (const font of fonts) {
+      names.push(font.loadedName);
+    }
+    names.push(loadTestFontId);
+
+    const div = this._document.createElement("div");
+    div.style.visibility = "hidden";
+    div.style.width = div.style.height = "10px";
+    div.style.position = "absolute";
+    div.style.top = div.style.left = "0px";
+
+    for (const name of names) {
+      const span = this._document.createElement("span");
+      span.textContent = "Hi";
+      span.style.fontFamily = name;
+      div.append(span);
+    }
+    this._document.body.append(div);
+
+    isFontReady(loadTestFontId, () => {
+      div.remove();
+      request.complete();
+    });
+    /** Hack end */
+  }
+}
 
 class FontFaceObject {
   constructor(