[Mac]Implement ViewID support. (third approach)

chrome/browser/cocoa/view_id_util.h

Index: chrome/browser/cocoa/view_id_util.h
diff --git a/chrome/browser/cocoa/view_id_util.h b/chrome/browser/cocoa/view_id_util.h
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+// 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_VIEW_ID_UTIL_H_
+#define CHROME_BROWSER_COCOA_VIEW_ID_UTIL_H_
+
+#import <Cocoa/Cocoa.h>
+
+#include "gfx/native_widget_types.h"
+#include "chrome/browser/view_ids.h"
+
+// ViewIDs are a system that indexes important views in the browser window by a
+// ViewID identifier (integer). This is a useful compatibility for finding a
+// view object in cross-platform tests. See BrowserFocusTest.* for an example
+// of how ViewIDs are used.
+
+// For views with fixed ViewIDs, we add a -viewID method to them to return their
+// ViewIDs directly. But for views with changeable ViewIDs, as NSView itself
+// doesn't provide a facility to store its ViewID, to avoid modifying each
+// individual classes for adding ViewID support, we use an internal map to store
+// ViewIDs of each view and provide some utility functions for NSView to
+// set/unset the ViewID and lookup a view with a specified ViewID.
+
+namespace view_id_util {
+
+// Associates the given ViewID with the view. It shall be called upon the view's
+// initialization.
+void SetID(NSView* view, ViewID viewID);
+
+// Removes the association between the view and its ViewID. It shall be called
+// just before the view's destruction.
+void UnsetID(NSView* view);
+
+// Returns the view with a specific ViewID in a window, or nil if no view in the
+// window has that ViewID.
+NSView* GetView(NSWindow* window, ViewID viewID);
+
+}  // namespace view_id_util
+
+
+@interface NSView (ViewID)
+
+// Returns the ViewID associated to the receiver. The default implementation
+// looks up the view's ViewID in the internal view to ViewID map. A subclass may
+// override this method to return its fixed ViewID.
+- (ViewID)viewID;
+
+@end
+
+#endif  // CHROME_BROWSER_COCOA_VIEW_ID_UTIL_H_