Fix NTP thumbnail generation

chrome/browser/thumbnails/thumbnailing_context.h

 // Copyright (c) 2013 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_THUMBNAILING_CONTEXT_H_
 #define CHROME_BROWSER_THUMBNAILS_THUMBNAILING_CONTEXT_H_
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/thumbnails/thumbnail_service.h"
 #include "components/history/core/common/thumbnail_score.h"
 #include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_observer.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace thumbnails {
 
 // The result of clipping. This can be used to determine if the
 // generated thumbnail is good or not.
 enum ClipResult {
   // Clipping is not done yet.
   CLIP_RESULT_UNPROCESSED,
   // The source image is smaller.
   CLIP_RESULT_SOURCE_IS_SMALLER,
   // Wider than tall by twice or more, clip horizontally.
   CLIP_RESULT_MUCH_WIDER_THAN_TALL,
   // Wider than tall, clip horizontally.
   CLIP_RESULT_WIDER_THAN_TALL,
   // Taller than wide, clip vertically.
   CLIP_RESULT_TALLER_THAN_WIDE,
   // The source and destination aspect ratios are identical.
   CLIP_RESULT_NOT_CLIPPED,
   // The source and destination are identical.
   CLIP_RESULT_SOURCE_SAME_AS_TARGET,
 };
 
 // Holds the information needed for processing a thumbnail.
-struct ThumbnailingContext : base::RefCountedThreadSafe<ThumbnailingContext> {
+struct ThumbnailingContext

[Lei Zhang, 2015/10/26 23:31:35]

This is looking a bit more complicated now. When in doubt, make it a class.

+    : base::RefCountedThreadSafe<ThumbnailingContext>,
+      content::WebContentsObserver {
   ThumbnailingContext(content::WebContents* web_contents,
                       ThumbnailService* receiving_service,
                       bool load_interrupted);
 
   // Create an instance for use with unit tests.
   static ThumbnailingContext* CreateThumbnailingContextForTest() {
     return new ThumbnailingContext();
   }
 
   scoped_refptr<ThumbnailService> service;
   GURL url;
   ClipResult clip_result;
   gfx::Size requested_copy_size;
   ThumbnailScore score;
 
  private:
   ThumbnailingContext();

[Lei Zhang, 2015/10/26 23:31:35]

Maybe just DISALLOW_IMPLICIT_CONSTRUCTORS?

   ~ThumbnailingContext();
 
   friend class base::RefCountedThreadSafe<ThumbnailingContext>;
 };
 
 }  // namespace thumbnails
 
 #endif  // CHROME_BROWSER_THUMBNAILS_THUMBNAILING_CONTEXT_H_