[Mac]Implement ViewID support.

chrome/browser/cocoa/button_with_viewid.mm

Index: chrome/browser/cocoa/button_with_viewid.mm
diff --git a/chrome/browser/cocoa/button_with_viewid.mm b/chrome/browser/cocoa/button_with_viewid.mm
new file mode 100644
index 0000000000000000000000000000000000000000..3eb92d2e11d7f12ce362c8797f970f76db32763d
--- /dev/null
+++ b/chrome/browser/cocoa/button_with_viewid.mm
@@ -0,0 +1,28 @@
+// 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.
+
+#import "chrome/browser/cocoa/button_with_viewid.h"
+
+#include "base/logging.h"
+#import "chrome/browser/cocoa/view_id_util.h"
+
+@implementation ButtonWithViewID
+
+@synthesize command = command_;
+
+// We use the tag property solely for VIewID support. So override this method
+// to avoid misuse of the tag property.
+- (void)setTag:(NSInteger)anInt {
+  NOTREACHED() <<
+      "NSView's tag is being used for ViewIDs. You are probably trying to use "
+      "them for some other purpose. See http://dev.chromium.org/developers/"
+      "design-documents/viewid-support-on-mac for details.";
+}
+
+- (void)setViewID:(ViewID)viewID {
+  // We call [super setTag:] here because it's overridden by us.
+  [super setTag:view_id_util::ViewIDToTag(viewID)];
+}
+
+@end  // @interface ButtonWithViewID