Bug 1539827 - Use cmd_selectAll instead of nsISelectionController.selectAll on action bar r=geckoview-reviewers,esawin

After bug 676268 is landed, Gecko/Android supports `text/html` mime type on
clipboard. But copy command is sometimes failed after select all is executed.

`nsISelectionContoller.selectAll` is different of `cmd_selectAll`.
Since `cmd_selectAll` that is used on Firefox desktop doesn't select root
element, copy command always works well. So we should use it like desktop
browser on Fennec.

Also, GV already uses cmd_selectAll on action bar, so this is Fennec only.

Differential Revision: https://phabricator.services.mozilla.com/D25924

--HG--
extra : moz-landing-system : lando

mobile/android/modules/ActionBarHandler.jsm

@@ -409,7 +409,7 @@ var ActionBarHandler = {
         }
 
         // Close ActionBarHandler, then selectAll, and display handles.
-        ActionBarHandler._getSelectAllController(element, win).selectAll();
+        ActionBarHandler._getDocShell(win).doCommand("cmd_selectAll");
         UITelemetry.addEvent("action.1", "actionbar", null, "select_all");
       },
     },
@@ -797,28 +797,6 @@ var ActionBarHandler = {
     return win.docShell.editingSession.getEditorForWindow(win);
   },
 
-  /**
-   * Returns a selection controller.
-   */
-  _getSelectionController: function(element = this._targetElement, win = this._contentWindow) {
-    if (this._isElementEditable(element)) {
-      return this._getEditor(element, win).selectionController;
-    }
-
-    return win.docShell.
-               QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsISelectionDisplay).
-               QueryInterface(Ci.nsISelectionController);
-  },
-
-  /**
-   * For selectAll(), provides the editor, or the default window selection Controller.
-   */
-  _getSelectAllController: function(element = this._targetElement, win = this._contentWindow) {
-    let editor = this._getEditor(element, win);
-    return (editor) ?
-      editor : this._getSelectionController(element, win);
-  },
-
   /**
    * Call / Phone Helper methods.
    */