Use std::unique_ptr to signal ownership transfer in WebCompositorSupport

cc/blink/web_content_layer_impl.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 CC_BLINK_WEB_CONTENT_LAYER_IMPL_H_
 #define CC_BLINK_WEB_CONTENT_LAYER_IMPL_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 13 matching lines @@
 class WebContentLayerClient;
 }
 
 namespace cc_blink {
 
 class WebContentLayerImpl : public blink::WebContentLayer,
                             public cc::ContentLayerClient {
  public:
   CC_BLINK_EXPORT explicit WebContentLayerImpl(blink::WebContentLayerClient*);
 
+  ~WebContentLayerImpl() override;
+
   // WebContentLayer implementation.
   blink::WebLayer* layer() override;
 
  protected:
-  ~WebContentLayerImpl() override;
-
   // ContentLayerClient implementation.
   gfx::Rect PaintableRegion() override;
   scoped_refptr<cc::DisplayItemList> PaintContentsToDisplayList(
       PaintingControlSetting painting_control) override;
   bool FillsBoundsCompletely() const override;
   size_t GetApproximateUnsharedMemoryUsage() const override;
 
   std::unique_ptr<WebLayerImpl> layer_;
   blink::WebContentLayerClient* client_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(WebContentLayerImpl);
 };
 
 }  // namespace cc_blink
 
 #endif  // CC_BLINK_WEB_CONTENT_LAYER_IMPL_H_