Fix NTP thumbnail generation

chrome/browser/thumbnails/thumbnail_tab_helper.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/thumbnails/thumbnail_tab_helper.h"
 
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/thumbnails/thumbnail_service.h"
 #include "chrome/browser/thumbnails/thumbnail_service_factory.h"
@@ skipping 48 matching lines @@
   gfx::Image image = gfx::Image::CreateFrom1xBitmap(thumbnail);
   context.service->SetPageThumbnail(context, image);
   DVLOG(1) << "Thumbnail taken for " << context.url << ": "
            << context.score.ToString();
 }
 
 void ProcessCapturedBitmap(scoped_refptr<ThumbnailingContext> context,
                            scoped_refptr<ThumbnailingAlgorithm> algorithm,
                            const SkBitmap& bitmap,
                            content::ReadbackResponse response) {
+  // Was the web contents destroyed before the thumbnail could be generated?
+  if (!context->web_contents())
+    return;
+
+  // Balance the IncrementCapturerCount() from UpdateThumbnailIfNecessary().
+  context->web_contents()->DecrementCapturerCount();
+
   if (response != content::READBACK_SUCCESS)
     return;
 
   // On success, we must be on the UI thread (on failure because of shutdown we
   // are not on the UI thread).
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
   algorithm->ProcessBitmap(context, base::Bind(&UpdateThumbnail), bitmap);
 }
 
-void AsyncProcessThumbnail(content::WebContents* web_contents,
-                           scoped_refptr<ThumbnailingContext> context,
+void AsyncProcessThumbnail(scoped_refptr<ThumbnailingContext> context,
                            scoped_refptr<ThumbnailingAlgorithm> algorithm) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
-  RenderWidgetHost* render_widget_host = web_contents->GetRenderViewHost();
+  RenderWidgetHost* render_widget_host =
+      context->web_contents()->GetRenderViewHost();
   content::RenderWidgetHostView* view = render_widget_host->GetView();
   if (!view)
     return;
   if (!view->IsSurfaceAvailableForCopy())
     return;
 
   gfx::Rect copy_rect = gfx::Rect(view->GetViewBounds().size());
   // Clip the pixels that will commonly hold a scrollbar, which looks bad in
   // thumbnails.
   int scrollbar_size = gfx::scrollbar_size();
@@ skipping 95 matching lines @@
 
   scoped_refptr<thumbnails::ThumbnailService> thumbnail_service =
       ThumbnailServiceFactory::GetForProfile(profile);
 
   // Skip if we don't need to update the thumbnail.
   if (thumbnail_service.get() == NULL ||
       !thumbnail_service->ShouldAcquirePageThumbnail(url)) {
     return;
   }
 
+  web_contents->IncrementCapturerCount(gfx::Size());
+
   scoped_refptr<thumbnails::ThumbnailingAlgorithm> algorithm(
       thumbnail_service->GetThumbnailingAlgorithm());
 
   scoped_refptr<ThumbnailingContext> context(new ThumbnailingContext(
       web_contents, thumbnail_service.get(), load_interrupted_));
-  AsyncProcessThumbnail(web_contents, context, algorithm);
+  AsyncProcessThumbnail(context, algorithm);
 }
 
 void ThumbnailTabHelper::RenderViewHostCreated(
     content::RenderViewHost* renderer) {
   // NOTIFICATION_WEB_CONTENTS_RENDER_VIEW_HOST_CREATED is really a new
   // RenderView, not RenderViewHost, and there is no good way to get
   // notifications of RenderViewHosts. So just be tolerant of re-registrations.
   bool registered = registrar_.IsRegistered(
       this,
       content::NOTIFICATION_RENDER_WIDGET_VISIBILITY_CHANGED,
       content::Source<RenderWidgetHost>(renderer));
   if (!registered) {
     registrar_.Add(
         this,
         content::NOTIFICATION_RENDER_WIDGET_VISIBILITY_CHANGED,
         content::Source<RenderWidgetHost>(renderer));
   }
 }
 
 void ThumbnailTabHelper::WidgetHidden(RenderWidgetHost* widget) {
   if (!enabled_)
     return;
   UpdateThumbnailIfNecessary(web_contents());
 }