Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/media/media_stream_video_capturer_source.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 CONTENT_RENDERER_MEDIA_MEDIA_STREAM_VIDEO_CAPTURER_SOURCE_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_VIDEO_CAPTURER_SOURCE_H_
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
@@ skipping 38 matching lines @@
       int max_requested_width,
       int max_requested_height,
       double max_requested_frame_rate,
       const VideoCaptureDeviceFormatsCB& callback) override;
   void StartSourceImpl(
       const media::VideoCaptureFormat& format,
       const blink::WebMediaConstraints& constraints,
       const VideoCaptureDeliverFrameCB& frame_callback) override;
   void StopSourceImpl() override;
 
-  // RenderFrame does NOT own this object. Avoid unintended multiple destruction
-  // by overriding RenderFrameObserver::OnDestruct().
+  // RenderFrameObserver implementation.
   void OnDestruct() final {}
 
   // Method to bind as RunningCallback in VideoCapturerSource::StartCapture().
   void OnStarted(bool result);
 
   const char* GetPowerLineFrequencyForTesting() const;
 
   // The source that provides video frames.
   const std::unique_ptr<media::VideoCapturerSource> source_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaStreamVideoCapturerSource);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_VIDEO_CAPTURER_SOURCE_H_