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

ppapi/shared_impl/media_stream_frame.h

 // 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.
 
 #ifndef PPAPI_SHARED_IMPL_MEDIA_STREAM_FRAME_H_
 #define PPAPI_SHARED_IMPL_MEDIA_STREAM_FRAME_H_
 
+#include "ppapi/c/ppb_audio_frame.h"
 #include "ppapi/c/ppb_video_frame.h"
 
 namespace ppapi {
 
 union MediaStreamFrame {
   enum Type {
     TYPE_UNKNOWN = 0,
     TYPE_AUDIO = 1,
     TYPE_VIDEO = 2,
   };
 
   struct Header {
     Type type;
     uint32_t size;
   };
 
   struct Audio {
     Header header;
-    // TODO(penghuang): implement the audio frame.
+    PP_TimeDelta timestamp;
+    PP_AudioFrame_SampleRate sample_rate;
+    uint32_t number_of_channels;
+    uint32_t number_of_samples;
+    uint32_t data_size;
+    // Uses 8 bytes to make sure the Audio struct has consistent size between
+    // NaCl code and renderer code.
+    uint8_t data[8];
   };
 
   struct Video {
     Header header;
     PP_TimeDelta timestamp;
     PP_VideoFrame_Format format;
     PP_Size size;
     uint32_t data_size;
     // Uses 8 bytes to make sure the Video struct has consistent size between
-    // Nacl code and renderer code.
+    // NaCl code and renderer code.
     uint8_t data[8];
   };
 
   // Because these structs are written and read in shared memory, we need
   // the size and alighment to be consistent between NaCl and its host trusted
   // platform.
   PP_COMPILE_ASSERT_SIZE_IN_BYTES(Header, 8);
-  PP_COMPILE_ASSERT_SIZE_IN_BYTES(Audio, 8);
+  PP_COMPILE_ASSERT_SIZE_IN_BYTES(Audio, 40);
   PP_COMPILE_ASSERT_SIZE_IN_BYTES(Video, 40);
 
   Header header;
   Video video;
   Audio audio;
 };
 
 }  // namespace ppapi
 
 #endif  // PPAPI_SHARED_IMPL_MEDIA_STREAM_FRAME_H_