Cast: Fix threading issues in VideoEncoderImpl

media/cast/video_sender/codecs/vp8/vp8_encoder.h

Index: media/cast/video_sender/codecs/vp8/vp8_encoder.h
diff --git a/media/cast/video_sender/codecs/vp8/vp8_encoder.h b/media/cast/video_sender/codecs/vp8/vp8_encoder.h
index e39bc1615667c30770dda9d71447962f3a06599f..a6dd396507ae50d875f4fb99a7c3586ff05ced5a 100644
--- a/media/cast/video_sender/codecs/vp8/vp8_encoder.h
+++ b/media/cast/video_sender/codecs/vp8/vp8_encoder.h
@@ -7,6 +7,7 @@
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/threading/thread_checker.h"
 #include "media/cast/cast_config.h"
 #include "third_party/libvpx/source/libvpx/vpx/vpx_encoder.h"
 
@@ -29,6 +30,10 @@ class Vp8Encoder {
 
   ~Vp8Encoder();
 
+  // Initialize the encoder before Encode() can be called. This method
+  // must be called on the thread that Encode() is called.
+  void Initialize();
+
   // Encode a raw image (as a part of a video stream).
   bool Encode(const scoped_refptr<media::VideoFrame>& video_frame,
               transport::EncodedVideoFrame* encoded_image);
@@ -83,6 +88,9 @@ class Vp8Encoder {
   bool acked_frame_buffers_[kNumberOfVp8VideoBuffers];
   Vp8Buffers last_used_vp8_buffer_;
   int number_of_repeated_buffers_;
+
+  // This is bound to the thread where Initialize() is called.
+  base::ThreadChecker thread_checker_;
 };
 
 }  // namespace cast