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

ppapi/shared_impl/media_stream_frame_buffer.cc

Index: ppapi/shared_impl/media_stream_frame_buffer.cc
diff --git a/ppapi/shared_impl/media_stream_frame_buffer.cc b/ppapi/shared_impl/media_stream_frame_buffer.cc
index 624883039ecb881504d6b9aa33b0e6adbe6538cb..4f556b54ae94a395072efc6bc63219ddc0effdd6 100644
--- a/ppapi/shared_impl/media_stream_frame_buffer.cc
+++ b/ppapi/shared_impl/media_stream_frame_buffer.cc
@@ -11,7 +11,8 @@ namespace ppapi {
 
 MediaStreamFrameBuffer::Delegate::~Delegate() {}
 
-void MediaStreamFrameBuffer::Delegate::OnNewFrameEnqueued() {
+bool MediaStreamFrameBuffer::Delegate::OnNewFramePreEnqueued(int32_t index) {
+  return false;
 }
 
 MediaStreamFrameBuffer::MediaStreamFrameBuffer(Delegate* delegate)
@@ -64,8 +65,8 @@ int32_t MediaStreamFrameBuffer::DequeueFrame() {
 void MediaStreamFrameBuffer::EnqueueFrame(int32_t index) {
   DCHECK_GE(index, 0);
   DCHECK_LT(index, number_of_frames_);
-  frame_queue_.push_back(index);
-  delegate_->OnNewFrameEnqueued();
+  if (!delegate_->OnNewFramePreEnqueued(index))
+    frame_queue_.push_back(index);
 }
 
 MediaStreamFrame* MediaStreamFrameBuffer::GetFramePointer(