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

ui/base/cocoa/hover_button.h

Index: ui/base/cocoa/hover_button.h
diff --git a/ui/base/cocoa/hover_button.h b/ui/base/cocoa/hover_button.h
index e665d3a6a7a1fd3e3d8c7e98f3b533738d2473ad..cadbf7ddb6fb38940622ed6f273b80ccb0c6d75d 100644
--- a/ui/base/cocoa/hover_button.h
+++ b/ui/base/cocoa/hover_button.h
@@ -23,16 +23,18 @@ UI_EXPORT
     kHoverStateMouseDown = 2
   };
 
-  HoverState hoverState_;
+  // Whether the user is mousing inside the button.
+  BOOL isMouseInside_;
 
  @private
   // Tracking area for button mouseover states. Nil if not enabled.
   ui::ScopedCrTrackingArea trackingArea_;
 }
 
-@property(nonatomic) HoverState hoverState;
+@property(nonatomic, assign) BOOL isMouseInside;
+@property(nonatomic, readonly) HoverState hoverState;
 
-// Enables or disables the tracking for the button.
+// Enables or disables the hover tracking for the button.
 - (void)setTrackingEnabled:(BOOL)enabled;
 
 // Checks to see whether the mouse is in the button's bounds and update