[Mac]Implement ViewID support.

chrome/browser/cocoa/download_shelf_view.mm

-// 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.
 
 #import "chrome/browser/cocoa/download_shelf_view.h"
 
 #include "base/scoped_nsobject.h"
 #include "chrome/browser/browser_theme_provider.h"
 #import "chrome/browser/cocoa/themed_window.h"
+#import "chrome/browser/cocoa/view_id_util.h"
 #include "grit/theme_resources.h"
 
 @implementation DownloadShelfView
 
 - (NSColor*)strokeColor {
   BOOL isKey = [[self window] isKeyWindow];
   ThemeProvider* themeProvider = [[self window] themeProvider];
   return themeProvider ? themeProvider->GetNSColor(
       isKey ? BrowserThemeProvider::COLOR_TOOLBAR_STROKE :
               BrowserThemeProvider::COLOR_TOOLBAR_STROKE_INACTIVE, true) :
@@ skipping 36 matching lines @@
   NSDivideRect([self bounds], &borderRect, &contentRect, 1, NSMaxYEdge);
   NSRectFillUsingOperation(borderRect, NSCompositeSourceOver);
 }
 
 // Mouse down events on the download shelf should not allow dragging the parent
 // window around.
 - (BOOL)mouseDownCanMoveWindow {
   return NO;
 }
 
+// Tag is used solely for ViewID. Override to prevent changing of it.
+- (NSInteger)tag {
+  return view_id_util::ViewIDToTag(VIEW_ID_DOWNLOAD_SHELF);
+}
+
 @end