Simplify content_layer attachment and viewporting logic.

chrome/browser/android/compositor/layer/thumbnail_layer.h

 // Copyright 2014 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_ANDROID_COMPOSITOR_LAYER_THUMBNAIL_LAYER_H_
 #define CHROME_BROWSER_ANDROID_COMPOSITOR_LAYER_THUMBNAIL_LAYER_H_
 
 #include <stddef.h>
 
 #include "base/macros.h"
@@ skipping 14 matching lines @@
 
 // A layer to render a thumbnail.
 class ThumbnailLayer : public Layer {
  public:
   // Creates a ThumbnailLayer.
   static scoped_refptr<ThumbnailLayer> Create();
   // Sets thumbnail that will be shown. |thumbnail| should not be nullptr.
   void SetThumbnail(Thumbnail* thumbnail);
   // Clip the thumbnail to the given |clipping|.
   void Clip(const gfx::Rect& clipping);
+  void ClearClip();
   // Add self to |parent| or replace self at |index| if there already is an
   // instance with the same ID at |index|.
   void AddSelfToParentOrReplaceAt(scoped_refptr<cc::Layer> parent,
                                   size_t index);
 
   // Implements Layer.
   scoped_refptr<cc::Layer> layer() override;
 
  protected:
   ThumbnailLayer();
   ~ThumbnailLayer() override;
 
  private:
   void UpdateSizes(const gfx::SizeF& content_size,
                    const gfx::SizeF& resource_size);
 
   scoped_refptr<cc::UIResourceLayer> layer_;
   gfx::SizeF content_size_;
   gfx::Rect last_clipping_;
+  bool clipped_ = false;
   gfx::SizeF resource_size_;
 
   DISALLOW_COPY_AND_ASSIGN(ThumbnailLayer);
 };
 
 }  // namespace android
 
 #endif  // CHROME_BROWSER_ANDROID_COMPOSITOR_LAYER_THUMBNAIL_LAYER_H_