[Mac]Implement ViewID support.

chrome/browser/cocoa/base_view.h

-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 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.
 
 #ifndef CHROME_BROWSER_COCOA_BASE_VIEW_H_
 #define CHROME_BROWSER_COCOA_BASE_VIEW_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/scoped_nsobject.h"
+#include "chrome/browser/view_ids.h"
 #include "gfx/rect.h"
 
 // A view that provides common functionality that many views will need:
 // - Automatic registration for mouse-moved events.
 // - Funneling of mouse and key events to two methods
 // - Coordinate conversion utilities
+// - ViewID support.
+//
+// We use NSView's tag property for ViewID support, BaseView class overrides
+// the tag method to return its ViewID value. So do not use the tag property
+// for other purpose in subclasses.
 
 @interface BaseView : NSView {
  @private
   NSTrackingArea *trackingArea_;
   BOOL dragging_;
   scoped_nsobject<NSEvent> pendingExitEvent_;
+  ViewID viewID_;
 }
 
+@property(assign, nonatomic) ViewID viewID;
+
 - (id)initWithFrame:(NSRect)frame;
 
 // Override these methods in a subclass.
 - (void)mouseEvent:(NSEvent *)theEvent;
 - (void)keyEvent:(NSEvent *)theEvent;
 
 // Useful rect conversions (doing coordinate flipping)
 - (gfx::Rect)NSRectToRect:(NSRect)rect;
 - (NSRect)RectToNSRect:(gfx::Rect)rect;
 
 @end
 
 #endif  // CHROME_BROWSER_COCOA_BASE_VIEW_H_