Reland change for aura tooltips that was revert due to build break:

ui/aura/aura.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 11 matching lines @@
       'defines': [
         'AURA_IMPLEMENTATION',
       ],
       'sources': [
         'aura_switches.cc',
         'aura_switches.h',
         'client/aura_constants.cc',
         'client/aura_constants.h',
         'client/drag_drop_client.h',
         'client/stacking_client.h',
+        'client/tooltip_client.h',
         'client/window_drag_drop_delegate.h',
         'cursor.h',
         'desktop_host.h',
         'desktop_host_linux.cc',
         'desktop_host_win.cc',
         'desktop_host_win.h',
         'desktop.cc',
         'desktop.h',
         'event.cc',
         'event.h',
@@ skipping 98 matching lines @@
       'conditions': [
         ['OS=="linux"', {
           'dependencies': [
             '<(DEPTH)/third_party/mesa/mesa.gyp:osmesa',
           ],
         }],
       ],
     },
   ],
 }