Makes the frame maximize button show the multi-state icon on hover.

ash/wm/workspace/frame_maximize_button.cc

 // 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.
 
 #include "ash/wm/workspace/frame_maximize_button.h"
 
 #include "ash/screen_ash.h"
 #include "ash/shell.h"
 #include "ash/wm/property_util.h"
 #include "ash/launcher/launcher.h"
@@ skipping 195 matching lines @@
           id = IDR_AURA_WINDOW_MAXIMIZED_SNAP_P;
           break;
         case SNAP_MINIMIZE:
           id = IDR_AURA_WINDOW_MAXIMIZED_SNAP_MINIMIZE_P;
           break;
         default:
           NOTREACHED();
       }
     }
     return *ResourceBundle::GetSharedInstance().GetImageNamed(id).ToSkBitmap();
+  } else if (state() == BS_HOT) {
+    return *ResourceBundle::GetSharedInstance().GetImageNamed(
+        IDR_AURA_WINDOW_MAXIMIZED_RESTORE_SNAP_P).ToSkBitmap();
   }
   return ImageButton::GetImageToPaint();
 }
 
 void FrameMaximizeButton::Cancel() {
   UninstallEventFilter();
   is_snap_enabled_ = false;
   phantom_window_.reset();
   snap_sizer_.reset();
   SchedulePaint();
@@ skipping 114 matching lines @@
       break;
     case SNAP_MINIMIZE:
       frame_->GetWidget()->Minimize();
       break;
     default:
       NOTREACHED();
   }
 }
 
 }  // namespace ash