Reland fix for thumbnail generation.

chrome/browser/thumbnails/thumbnail_tab_helper.h

 // 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.
 
 #ifndef CHROME_BROWSER_THUMBNAILS_THUMBNAIL_TAB_HELPER_H_
 #define CHROME_BROWSER_THUMBNAILS_THUMBNAIL_TAB_HELPER_H_
 
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 #include "chrome/browser/thumbnails/thumbnailing_context.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/readback_types.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
 namespace content {
 class RenderViewHost;
 class RenderWidgetHost;
@@ skipping 13 matching lines @@
   // content::NotificationObserver overrides.
   void Observe(int type,
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
   // content::WebContentsObserver overrides.
   void RenderViewDeleted(content::RenderViewHost* render_view_host) override;
   void DidStartLoading() override;
   void NavigationStopped() override;
 
+  // Clean up after thumbnail generation has ended.

[Lei Zhang, 2016/01/12 01:54:46]

Might be good to put this list in chronological order, since these are declared
here. Whereas before, they were in reverse order in the anonymous namespace to
avoid the need to forward declare. The ordering in the .cpp should be flipped as
well.

UpdateThumbnailIfNecessary()
AsyncProcessThumbnail()
ProcessCapturedBitmap()
UpdateThumbnail()
CleanUpFromThumbnailGeneration()

[shrike, 2016/01/12 19:52:39]

OK.

+  void CleanUpFromThumbnailGeneration();
+
+  // Pass the thumbnail to the thumbnail service.
+  void UpdateThumbnail(
+      const thumbnails::ThumbnailingContext& context,
+      const SkBitmap& thumbnail);
+
+  // Create a thumbnail from the web contents bitmap.
+  void ProcessCapturedBitmap(
+      scoped_refptr<thumbnails::ThumbnailingAlgorithm> algorithm,
+      const SkBitmap& bitmap,
+      content::ReadbackResponse response);
+
+  // Initiate asynchronous generation of a thumbnail from the web contents.
+  void AsyncProcessThumbnail(
+      scoped_refptr<thumbnails::ThumbnailService> thumbnail_service);
+
   // Update the thumbnail of the given tab contents if necessary.
-  void UpdateThumbnailIfNecessary(content::WebContents* web_contents);
+  void UpdateThumbnailIfNecessary();
 
   // Called when a render view host was created for a WebContents.
   void RenderViewHostCreated(content::RenderViewHost* renderer);
 
   // Indicates that the given widget has changed is visibility.
   void WidgetHidden(content::RenderWidgetHost* widget);
 
   content::NotificationRegistrar registrar_;
+  scoped_refptr<thumbnails::ThumbnailingContext> thumbnailing_context_;
 
   bool load_interrupted_;
 
+  base::WeakPtrFactory<ThumbnailTabHelper> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(ThumbnailTabHelper);
 };
 
 #endif  // CHROME_BROWSER_THUMBNAILS_THUMBNAIL_TAB_HELPER_H_