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

ppapi/shared_impl/media_stream_frame_buffer.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/shared_impl/media_stream_frame_buffer.h"
 
 #include "base/logging.h"
 #include "ppapi/c/pp_errors.h"
 
 namespace ppapi {
 
 MediaStreamFrameBuffer::Delegate::~Delegate() {}
 
-void MediaStreamFrameBuffer::Delegate::OnNewFrameEnqueued() {
+bool MediaStreamFrameBuffer::Delegate::OnNewFramePreEnqueued(int32_t index) {
+  return false;
 }
 
 MediaStreamFrameBuffer::MediaStreamFrameBuffer(Delegate* delegate)
    : delegate_(delegate),
      frame_size_(0),
      number_of_frames_(0) {
   DCHECK(delegate_);
 }
 
 MediaStreamFrameBuffer::~MediaStreamFrameBuffer() {
@@ skipping 32 matching lines @@
   if (frame_queue_.empty())
     return PP_ERROR_FAILED;
   int32_t frame = frame_queue_.front();
   frame_queue_.pop_front();
   return frame;
 }
 
 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(
     int32_t index) {
   DCHECK_GE(index, 0);
   DCHECK_LT(index, number_of_frames_);
   return frames_[index];
 }
 
 }  // namespace ppapi