Implement caret annotations

The file `test/pdfs/annotation-caret-ink.pdf` is already available in
the repository as a reference test for this since I supplied it for
another patch that implemented ink annotations.

src/core/annotation.js

@@ -107,6 +107,9 @@ class AnnotationFactory {
       case 'Polygon':
         return new PolygonAnnotation(parameters);
 
+      case 'Caret':
+        return new CaretAnnotation(parameters);
+
       case 'Ink':
         return new InkAnnotation(parameters);
 
@@ -1026,6 +1029,15 @@ class PolygonAnnotation extends PolylineAnnotation {
   }
 }
 
+class CaretAnnotation extends Annotation {
+  constructor(parameters) {
+    super(parameters);
+
+    this.data.annotationType = AnnotationType.CARET;
+    this._preparePopup(parameters.dict);
+  }
+}
+
 class InkAnnotation extends Annotation {
   constructor(parameters) {
     super(parameters);

src/display/annotation_layer.js

@@ -83,6 +83,9 @@ class AnnotationElementFactory {
       case AnnotationType.POLYLINE:
         return new PolylineAnnotationElement(parameters);
 
+      case AnnotationType.CARET:
+        return new CaretAnnotationElement(parameters);
+
       case AnnotationType.INK:
         return new InkAnnotationElement(parameters);
 
@@ -1017,6 +1020,30 @@ class PolygonAnnotationElement extends PolylineAnnotationElement {
   }
 }
 
+class CaretAnnotationElement extends AnnotationElement {
+  constructor(parameters) {
+    const isRenderable = !!(parameters.data.hasPopup ||
+                            parameters.data.title || parameters.data.contents);
+    super(parameters, isRenderable, /* ignoreBorder = */ true);
+  }
+
+  /**
+   * Render the caret annotation's HTML element in the empty container.
+   *
+   * @public
+   * @memberof CaretAnnotationElement
+   * @returns {HTMLSectionElement}
+   */
+  render() {
+    this.container.className = 'caretAnnotation';
+
+    if (!this.data.hasPopup) {
+      this._createPopup(this.container, null, this.data);
+    }
+    return this.container;
+  }
+}
+
 class InkAnnotationElement extends AnnotationElement {
   constructor(parameters) {
     let isRenderable = !!(parameters.data.hasPopup ||

web/annotation_layer_builder.css

@@ -188,6 +188,7 @@
 .annotationLayer .circleAnnotation svg ellipse,
 .annotationLayer .polylineAnnotation svg polyline,
 .annotationLayer .polygonAnnotation svg polygon,
+.annotationLayer .caretAnnotation,
 .annotationLayer .inkAnnotation svg polyline,
 .annotationLayer .stampAnnotation,
 .annotationLayer .fileAttachmentAnnotation {