[PPAPI] Pepper MediaStream API audio track implementation and example.

ppapi/shared_impl/media_stream_frame_buffer.h

Index: ppapi/shared_impl/media_stream_frame_buffer.h
diff --git a/ppapi/shared_impl/media_stream_frame_buffer.h b/ppapi/shared_impl/media_stream_frame_buffer.h
index e95084642c03bc20a2ae32b452df4f0a88ca8c4d..ab46b272a55ec0ddc4c1e789c1454d6e4e441dfb 100644
--- a/ppapi/shared_impl/media_stream_frame_buffer.h
+++ b/ppapi/shared_impl/media_stream_frame_buffer.h
@@ -11,6 +11,7 @@
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/shared_memory.h"
+#include "base/synchronization/lock.h"
 #include "ppapi/shared_impl/media_stream_frame.h"
 #include "ppapi/shared_impl/ppapi_shared_export.h"
 
@@ -48,9 +49,15 @@ class PPAPI_SHARED_EXPORT MediaStreamFrameBuffer {
 
   ~MediaStreamFrameBuffer();
 
-  int32_t number_of_frames() const { return number_of_frames_; }
+  int32_t number_of_frames() const {
+    base::AutoLock lock(mutex_);
+    return number_of_frames_;
+  }
 
-  int32_t frame_size() const { return frame_size_; }
+  int32_t frame_size() const {
+    base::AutoLock lock(mutex_);
+    return frame_size_;
+  }
 
   // Initializes shared memory for frames transmission.
   bool SetFrames(int32_t number_of_frames,
@@ -70,6 +77,9 @@ class PPAPI_SHARED_EXPORT MediaStreamFrameBuffer {
  private:
   Delegate* delegate_;
 
+  // A mutex to protect below fields.
+  mutable base::Lock mutex_;
+
   // A queue of frame indexes.
   std::deque<int32_t> frame_queue_;