Refactor RenderWidgetHost::set_paint_observer()

chrome/browser/ui/cocoa/tabpose_window.mm

 // 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/ui/cocoa/tabpose_window.h"
 
 #import <QuartzCore/QuartzCore.h>
 
 #include "app/resource_bundle.h"
 #include "base/mac_util.h"
@@ skipping 98 matching lines @@
     ResetPaintingObserver();
   }
 
   void DidReceiveBitmap(const SkBitmap& bitmap) {
     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
     ResetPaintingObserver();
     [layer_ setThumbnail:bitmap];
   }
 
   void ResetPaintingObserver() {
-    if (rwh_->painting_observer() != NULL) {
-      DCHECK(rwh_->painting_observer() ==
-             g_browser_process->GetThumbnailGenerator());
-      rwh_->set_painting_observer(NULL);
-    }
+    g_browser_process->GetThumbnailGenerator()->MonitorRenderer(rwh_, false);
   }
 
   gfx::Size size_;
   RenderWidgetHost* rwh_;  // weak
   ThumbnailLayer* layer_;  // weak, owns us
   base::ScopedCallbackFactory<ThumbnailLoader> factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ThumbnailLoader);
 };
 
@@ skipping 1411 matching lines @@
   tile.set_tab_contents(contents->tab_contents());
   ThumbnailLayer* thumbLayer = [allThumbnailLayers_ objectAtIndex:index];
   [thumbLayer setTabContents:contents->tab_contents()];
 }
 
 - (void)tabStripModelDeleted {
   [self close];
 }
 
 @end