Enable tooltips for aura.

ui/aura_shell/aura_shell.gyp

 # Copyright (c) 2011 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
 
   'targets': [
@@ skipping 15 matching lines @@
         '../gfx/compositor/compositor.gyp:compositor',
         '../ui.gyp:ui',
         '../ui.gyp:ui_resources',
         '../ui.gyp:ui_resources_standard',
       ],
       'defines': [
         'AURA_SHELL_IMPLEMENTATION',
       ],
       'sources': [
         # All .cc, .h under views, except unittests
+        'aura_constants.h',
         'default_container_event_filter.cc',
         'default_container_event_filter.h',
         'default_container_layout_manager.cc',
         'default_container_layout_manager.h',
         'desktop_background_view.cc',
         'desktop_background_view.h',
         'desktop_layout_manager.cc',
         'desktop_layout_manager.h',
         'launcher/app_launcher_button.cc',
         'launcher/app_launcher_button.h',
@@ skipping 122 matching lines @@
         '../../views/views.gyp:views_desktop',
         '../../views/views.gyp:views_desktop_lib',
         '../../views/views.gyp:views_unittests',
         '../aura/aura.gyp:*',
         '../gfx/compositor/compositor.gyp:*',
         'aura_shell_exe',
       ],
     },
   ],
 }