[Chromium addon] Add the Page scrolling mode to the options (PR 14112 follow-up)

extensions/chromium/options/options.html

@@ -153,6 +153,7 @@ body {
     <span></span>
     <select>
       <option value="-1">Default</option>
+      <option value="3">Page scrolling</option>
       <option value="0">Vertical scrolling</option>
       <option value="1">Horizontal scrolling</option>
       <option value="2">Wrapped scrolling</option>

extensions/chromium/preferences_schema.json

@@ -186,13 +186,14 @@
     },
     "scrollModeOnLoad": {
       "title": "Scroll mode on load",
-      "description": "Controls how the viewer scrolls upon load.\n -1 = Default (uses the last position if available/enabled).\n 0 = Vertical scrolling.\n 1 = Horizontal scrolling.\n 2 = Wrapped scrolling.",
+      "description": "Controls how the viewer scrolls upon load.\n -1 = Default (uses the last position if available/enabled).\n 3 = Page scrolling.\n 0 = Vertical scrolling.\n 1 = Horizontal scrolling.\n 2 = Wrapped scrolling.",
       "type": "integer",
       "enum": [
         -1,
         0,
         1,
-        2
+        2,
+        3
       ],
       "default": -1
     },