[Mac] Prevent a crash with the DownloadStartedAnimation.

chrome/browser/cocoa/download_started_animation_mac.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.
 //
 // This file contains the Mac implementation the download animation, displayed
 // at the start of a download. The animation produces an arrow pointing
 // downwards and animates towards the bottom of the window where the new
 // download appears in the download shelf.
 
 #include "chrome/browser/download/download_started_animation.h"
 
@@ skipping 157 matching lines @@
 
 - (void)animationComplete {
   [[animation_ parentWindow] removeChildWindow:animation_];
   [self release];
 }
 
 + (void)startAnimationWithTabContents:(TabContents*)contents {
   // Will be deleted when the animation is complete in -animationComplete.
   DownloadStartedAnimationMac* controller =
       [[self alloc] initWithTabContents:contents];
+  // The initializer can return nil.
+  if (!controller)
+    return;
+
   // The |animation_| releaes itself when done.
   [controller->animation_ startAnimation];
 }
 
 @end
 
 void DownloadStartedAnimation::Show(TabContents* tab_contents) {
   DCHECK(tab_contents);
 
   // Will be deleted when the animation is complete.
   [DownloadStartedAnimationMac startAnimationWithTabContents:tab_contents];
 }