Make virtual method pure virtual

android_webview/browser/compositor_frame_consumer.h

 // Copyright 2016 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 ANDROID_WEBVIEW_BROWSER_COMPOSITOR_FRAME_CONSUMER_H_
 #define ANDROID_WEBVIEW_BROWSER_COMPOSITOR_FRAME_CONSUMER_H_
 
 #include <map>
 
 #include "android_webview/browser/child_frame.h"
@@ skipping 25 matching lines @@
   // The producer is responsible for managing the relationship with its
   // consumers. The only exception to this is when a consumer is explicitly
   // destroyed, at which point it needs to inform its producer.
   // In order to register a consumer with a new producer, the current producer
   // must unregister the consumer, and call SetCompositorProducer(nullptr).
   virtual void SetCompositorFrameProducer(
       CompositorFrameProducer* compositor_frame_producer) = 0;
   virtual void SetScrollOffsetOnUI(gfx::Vector2d scroll_offset) = 0;
   // Returns uncommitted frame to be returned, if any.
   virtual std::unique_ptr<ChildFrame> SetFrameOnUI(
-      std::unique_ptr<ChildFrame> frame);
+      std::unique_ptr<ChildFrame> frame) = 0;
   virtual void InitializeHardwareDrawIfNeededOnUI() = 0;
   virtual ParentCompositorDrawConstraints GetParentDrawConstraintsOnUI()
       const = 0;
   virtual void SwapReturnedResourcesOnUI(
       ReturnedResourcesMap* returned_resource_map) = 0;
   virtual bool ReturnedResourcesEmptyOnUI() const = 0;
   virtual ChildFrameQueue PassUncommittedFrameOnUI() = 0;
   virtual bool HasFrameOnUI() const = 0;
   virtual void DeleteHardwareRendererOnUI() = 0;
 
  protected:
   virtual ~CompositorFrameConsumer() {}
 };
 
 }  // namespace android_webview
 
 #endif  // ANDROID_WEBVIEW_BROWSER_COMPOSITOR_FRAME_PRODUCER_H_