[edition] Add a FreeText editor (mozilla#14970)

- add a basic UI to edit some text in a pdf;
- an editor can be moved, suppressed, cut, copied, pasted, selected;
- add an undo/redo manager.

extensions/chromium/preferences_schema.json

@@ -160,6 +160,10 @@
       ],
       "default": 2
     },
+    "annotationEditorEnabled": {
+      "type": "boolean",
+      "default": false
+    },
     "enablePermissions": {
       "type": "boolean",
       "default": false

l10n/en-US/viewer.properties

@@ -249,3 +249,10 @@ password_cancel=Cancel
 printing_not_supported=Warning: Printing is not fully supported by this browser.
 printing_not_ready=Warning: The PDF is not fully loaded for printing.
 web_fonts_disabled=Web fonts are disabled: unable to use embedded PDF fonts.
+
+# Editor
+editor_none.title=Disable Annotation Editing
+editor_none_label=Disable Editing
+freetext_default_content=Enter some text…
+editor_free_text.title=Add FreeText Annotation
+editor_free_text_label=FreeText Annotation

src/display/annotation_storage.js

@@ -13,6 +13,7 @@
  * limitations under the License.
  */
 
+import { AnnotationEditor } from "./editor/editor.js";
 import { MurmurHash3_64 } from "../shared/murmurhash3.js";
 import { objectFromMap } from "../shared/util.js";
 
@@ -62,6 +63,14 @@ class AnnotationStorage {
     return this._storage.get(key);
   }
 
+  /**
+   * Remove a value from the storage.
+   * @param {string} key
+   */
+  removeKey(key) {
+    this._storage.delete(key);
+  }
+
   /**
    * Set the value for a given key
    *
@@ -123,7 +132,19 @@ class AnnotationStorage {
    * @ignore
    */
   get serializable() {
-    return this._storage.size > 0 ? this._storage : null;
+    if (this._storage.size === 0) {
+      return null;
+    }
+
+    const clone = new Map();
+    for (const [key, value] of this._storage) {
+      if (value instanceof AnnotationEditor) {
+        clone.set(key, value.serialize());
+      } else {
+        clone.set(key, value);
+      }
+    }
+    return clone;
   }
 
   /**