cc: Various code safety improvements in video compositing code.

cc/layers/video_frame_provider_client_impl.h

Index: cc/layers/video_frame_provider_client_impl.h
diff --git a/cc/layers/video_frame_provider_client_impl.h b/cc/layers/video_frame_provider_client_impl.h
index 39f66fb009db00e81960b3099c243495f8f58f02..2688ad25d8cb8332986348274a451d3cc531a607 100644
--- a/cc/layers/video_frame_provider_client_impl.h
+++ b/cc/layers/video_frame_provider_client_impl.h
@@ -8,6 +8,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
+#include "cc/base/cc_export.h"
 #include "cc/layers/video_frame_provider.h"
 #include "ui/gfx/transform.h"
 
@@ -16,42 +17,53 @@ namespace media { class VideoFrame; }
 namespace cc {
 class VideoLayerImpl;
 
-class VideoFrameProviderClientImpl
+// VideoFrameProviderClientImpl liasons with the VideoFrameProvider and the
+// VideoLayer. It receives updates from the provider and updates the layer as a
+// result. It also allows the layer to access the video frame that the provider
+// has.
+class CC_EXPORT VideoFrameProviderClientImpl
     : public VideoFrameProvider::Client,
       public base::RefCounted<VideoFrameProviderClientImpl> {
  public:
+  // Must be created on the impl thread while the main thread is blocked.
   static scoped_refptr<VideoFrameProviderClientImpl> Create(
       VideoFrameProvider* provider);
 
-  VideoLayerImpl* active_video_layer() { return active_video_layer_; }
+  VideoLayerImpl* ActiveVideoLayer() const;
   void SetActiveVideoLayer(VideoLayerImpl* video_layer);
 
+  bool Stopped() const;
+  // Must be called on the impl thread while the main thread is blocked.
   void Stop();
-  bool Stopped();
 
   scoped_refptr<media::VideoFrame> AcquireLockAndCurrentFrame();
   void PutCurrentFrame(const scoped_refptr<media::VideoFrame>& frame);
   void ReleaseLock();
-  const gfx::Transform& stream_texture_matrix() const {
-    return stream_texture_matrix_;
-  }
 
-  // VideoFrameProvider::Client implementation. These methods are all callable
-  // on any thread.
+  const gfx::Transform& StreamTextureMatrix() const;
+
+  // VideoFrameProvider::Client implementation.
+  // Called on the main thread.
   void StopUsingProvider() override;
+  // Called on the impl thread.
   void DidReceiveFrame() override;
   void DidUpdateMatrix(const float* matrix) override;
 
  private:
-  explicit VideoFrameProviderClientImpl(VideoFrameProvider* provider);
   friend class base::RefCounted<VideoFrameProviderClientImpl>;
+
+  explicit VideoFrameProviderClientImpl(VideoFrameProvider* provider);
   ~VideoFrameProviderClientImpl() override;
 
+  VideoFrameProvider* provider_;
   VideoLayerImpl* active_video_layer_;
+  bool stopped_;
 
-  // Guards the destruction of provider_ and the frame that it provides
+  // Since the provider lives on another thread, it can be destroyed while the
+  // frame controller are accessing its frame. Before being destroyed the
+  // provider calls StopUsingProvider. provider_lock_ blocks StopUsingProvider
+  // from returning until the frame controller is done using the frame.
   base::Lock provider_lock_;
-  VideoFrameProvider* provider_;
   base::ThreadChecker thread_checker_;
 
   gfx::Transform stream_texture_matrix_;