Drive: Add "Clear Local Cache" in the Gear menu to clear all local cache of Drive.

chrome/browser/resources/file_manager/js/mock_chrome.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 function MockEventSource() {
   this.listeners_ = [];
 }
 
 /**
  * Add a listener.
@@ skipping 525 matching lines @@
       COPY_BUTTON_LABEL: 'Copy',
       CUT_BUTTON_LABEL: 'Cut',
 
       UNMOUNT_FAILED: 'Unable to eject: $1',
       UNMOUNT_DEVICE_BUTTON_LABEL: 'Unmount',
       FORMAT_DEVICE_BUTTON_LABEL: 'Format',
 
       GDATA_MENU_HELP: 'Help',
       GDATA_MOBILE_CONNECTION_OPTION: 'Do not use mobile data for sync',
       GDATA_SHOW_HOSTED_FILES_OPTION: 'Show Google Docs files',
+      GDATA_CLEAR_LOCAL_CACHE: 'Clear local cache',
       GDATA_WAITING_FOR_SPACE_INFO: 'Waiting for space info...',
       GDATA_FAILED_SPACE_INFO: 'Failed to retrieve space info',
       GDATA_BUY_MORE_SPACE: 'Buy more storage...',
       GDATA_SPACE_AVAILABLE: '$1 left',
 
       OFFLINE_COLUMN_LABEL: 'Available offline',
       GDATA_LOADING: 'Hang with us. We\'re fetching your files.',
       GDATA_RETRY: 'Retry',
       GDATA_LEARN_MORE: 'Learn more',
       GDATA_CANNOT_REACH: '$1 cannot be reached at this time',
@@ skipping 245 matching lines @@
 
   setWindowHeight: function(height) {
     this.popup_.style.height = height + 'px';
   },
 
   closeWindow: function() {
     this.popup_.parentNode.removeChild(this.popup_);
     this.popup_ = null;
   }
 };