Revert of [Mojo Video Capture] Simplify media::VideoCaptureDevice::Client:Buffer to a struct

media/capture/video/video_capture_buffer_tracker.h

Index: media/capture/video/video_capture_buffer_tracker.h
diff --git a/media/capture/video/video_capture_buffer_tracker.h b/media/capture/video/video_capture_buffer_tracker.h
index 418492f154c4bf96d413cd482dbffa32877b976b..3e3d7bf888a2ff37aacdd53963c80476ea1f3c98 100644
--- a/media/capture/video/video_capture_buffer_tracker.h
+++ b/media/capture/video/video_capture_buffer_tracker.h
@@ -50,7 +50,9 @@
   void set_frame_feedback_id(int value) { frame_feedback_id_ = value; }
   int frame_feedback_id() { return frame_feedback_id_; }
 
-  virtual std::unique_ptr<VideoCaptureBufferHandle> GetMemoryMappedAccess() = 0;
+  // Returns a scoped handle to the underlying storage.
+  virtual std::unique_ptr<VideoCaptureBufferHandle> GetBufferHandle() = 0;
+
   virtual mojo::ScopedSharedBufferHandle GetHandleForTransit() = 0;
 
  private: