Speculative revert by sheriff

cc/layers/video_frame_provider.h

 // Copyright (c) 2012 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_LAYERS_VIDEO_FRAME_PROVIDER_H_
 #define CC_LAYERS_VIDEO_FRAME_PROVIDER_H_
 
 #include "base/memory/ref_counted.h"
-#include "base/time/time.h"
 #include "cc/base/cc_export.h"
 
 namespace media {
 class VideoFrame;
 }
 
 namespace cc {
 
-// VideoFrameProvider and VideoFrameProvider::Client define the relationship by
-// which video frames are exchanged between a provider and client.
-//
-// Threading notes: This class may be used in a multithreaded manner. However,
-// if the Client implementation calls GetCurrentFrame()/PutCurrentFrame() from
-// one thread, the provider must ensure that all client methods (except
-// StopUsingProvider()) are called from that thread (typically the compositor
-// thread).
+// Threading notes: This class may be used in a multi threaded manner.
+// Specifically, the implementation may call GetCurrentFrame() or
+// PutCurrentFrame() from the compositor thread. If so, the caller is
+// responsible for making sure Client::DidReceiveFrame() and
+// Client::DidUpdateMatrix() are only called from this same thread.
 class CC_EXPORT VideoFrameProvider {
  public:
+  virtual ~VideoFrameProvider() {}
+
   class CC_EXPORT Client {
    public:
-    // The provider will call this method to tell the client to stop using it.
+    // Provider will call this method to tell the client to stop using it.
     // StopUsingProvider() may be called from any thread. The client should
     // block until it has PutCurrentFrame() any outstanding frames.
     virtual void StopUsingProvider() = 0;
 
-    // Notifies the client that it should start or stop making regular
-    // UpdateCurrentFrame() calls to the provider. No further calls to
-    // UpdateCurrentFrame() should be made once StopRendering() returns.
-    //
-    // Callers should use these methods to indicate when it expects and no
-    // longer expects (respectively) to have new frames for the client. Clients
-    // may use this information for power conservation.
-    virtual void StartRendering() = 0;
-    virtual void StopRendering() = 0;
-
-    // Notifies the client that GetCurrentFrame() will return new data.
-    // TODO(dalecurtis): Nuke this once VideoFrameProviderClientImpl is using a
-    // BeginFrameObserver based approach. http://crbug.com/336733
+    // Notifies the provider's client that a call to GetCurrentFrame() will
+    // return new data.
     virtual void DidReceiveFrame() = 0;
 
-    // Notifies the client of a new UV transform matrix to be used.
+    // Notifies the provider's client of a new UV transform matrix to be used.
     virtual void DidUpdateMatrix(const float* matrix) = 0;
 
    protected:
     virtual ~Client() {}
   };
 
   // May be called from any thread, but there must be some external guarantee
   // that the provider is not destroyed before this call returns.
   virtual void SetVideoFrameProviderClient(Client* client) = 0;
 
-  // Called by the client on a regular interval. Returns true if a new frame
-  // will be available via GetCurrentFrame() which should be displayed within
-  // the presentation interval [|deadline_min|, |deadline_max|].
-  //
-  // Implementations may use this to drive frame acquisition from underlying
-  // sources, so it must be called by clients before calling GetCurrentFrame().
-  virtual bool UpdateCurrentFrame(base::TimeTicks deadline_min,
-                                  base::TimeTicks deadline_max) = 0;
-
-  // Returns the current frame, which may have been updated by a recent call to
-  // UpdateCurrentFrame(). A call to this method does not ensure that the frame
-  // will be rendered. A subsequent call to PutCurrentFrame() must be made if
-  // the frame is expected to be rendered.
-  //
-  // Clients should call this in response to UpdateCurrentFrame() returning true
-  // or in response to a DidReceiveFrame() call.
-  //
-  // TODO(dalecurtis): Remove text about DidReceiveFrame() once the old path
-  // has been removed. http://crbug.com/439548
+  // This function places a lock on the current frame and returns a pointer to
+  // it. Calls to this method should always be followed with a call to
+  // PutCurrentFrame().
+  // Only the current provider client should call this function.
   virtual scoped_refptr<media::VideoFrame> GetCurrentFrame() = 0;
 
-  // Indicates that the last frame returned via GetCurrentFrame() is expected to
-  // be rendered. Must only occur after a previous call to GetCurrentFrame().
-  virtual void PutCurrentFrame() = 0;
-
- protected:
-  virtual ~VideoFrameProvider() {}
+  // This function releases the lock on the video frame. It should always be
+  // called after GetCurrentFrame(). Frames passed into this method
+  // should no longer be referenced after the call is made. Only the current
+  // provider client should call this function.
+  virtual void PutCurrentFrame(
+      const scoped_refptr<media::VideoFrame>& frame) = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_VIDEO_FRAME_PROVIDER_H_