[Mac] Reimplement HoverButton and HoverImageButton using NSButton.state.

ui/message_center/cocoa/tray_view_controller.mm

Index: ui/message_center/cocoa/tray_view_controller.mm
diff --git a/ui/message_center/cocoa/tray_view_controller.mm b/ui/message_center/cocoa/tray_view_controller.mm
index 98f378c88307c2f2d54ca65449e09788d81f21c8..128c6dfa048ca970c5db3b2e8fddd05ef4fd78fa 100644
--- a/ui/message_center/cocoa/tray_view_controller.mm
+++ b/ui/message_center/cocoa/tray_view_controller.mm
@@ -178,17 +178,12 @@ const CGFloat kTrayBottomMargin = 75;
 }
 
 - (void)toggleQuietMode:(id)sender {
-  ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
   if (messageCenter_->IsQuietMode()) {
     messageCenter_->SetQuietMode(false);
     [pauseButton_ setTrackingEnabled:YES];
-    [pauseButton_ setDefaultImage:
-        rb.GetNativeImageNamed(IDR_NOTIFICATION_PAUSE).ToNSImage()];
   } else {
     messageCenter_->EnterQuietModeWithExpire(base::TimeDelta::FromDays(1));
     [pauseButton_ setTrackingEnabled:NO];
-    [pauseButton_ setDefaultImage:
-        rb.GetNativeImageNamed(IDR_NOTIFICATION_PAUSE_PRESSED).ToNSImage()];
   }
 }
 
@@ -315,6 +310,7 @@ const CGFloat kTrayBottomMargin = 75;
       NSMinX(clearAllButtonFrame) - kButtonXMargin,
       defaultImage);
   pauseButton_.reset([[HoverImageButton alloc] initWithFrame:pauseButtonFrame]);
+  [pauseButton_ setButtonType:NSToggleButton];
   [pauseButton_ setDefaultImage:defaultImage];
   [pauseButton_ setHoverImage:
       rb.GetNativeImageNamed(IDR_NOTIFICATION_PAUSE_HOVER).ToNSImage()];