Initialize cc::VideoFrameProviderClientImpl::active_video_layer_ to NULL.

cc/test/fake_video_frame_provider.h

Index: cc/test/fake_video_frame_provider.h
diff --git a/cc/test/fake_video_frame_provider.h b/cc/test/fake_video_frame_provider.h
index 972d8f8853323fe767763a942a54ee9fbe53396a..fc462e4a03981b702cca03e70d8f174b12cf0aeb 100644
--- a/cc/test/fake_video_frame_provider.h
+++ b/cc/test/fake_video_frame_provider.h
@@ -21,6 +21,8 @@ class FakeVideoFrameProvider : public VideoFrameProvider {
   virtual void PutCurrentFrame(const scoped_refptr<media::VideoFrame>&)
       OVERRIDE {}
 
+  Client* client() { return client_; }
+
   void set_frame(const scoped_refptr<media::VideoFrame>& frame) {
     frame_ = frame;
   }