Add support for 3-byte headers in VideoToolbox NALU parser.

webrtc/modules/video_coding/codecs/h264/h264_video_toolbox_nalu.h

Index: webrtc/modules/video_coding/codecs/h264/h264_video_toolbox_nalu.h
diff --git a/webrtc/modules/video_coding/codecs/h264/h264_video_toolbox_nalu.h b/webrtc/modules/video_coding/codecs/h264/h264_video_toolbox_nalu.h
index 50942536f3d26e0725dc37da7c21d7af48eaa14f..7862c3b61830e873e91336b14ee26d23307eb947 100644
--- a/webrtc/modules/video_coding/codecs/h264/h264_video_toolbox_nalu.h
+++ b/webrtc/modules/video_coding/codecs/h264/h264_video_toolbox_nalu.h
@@ -17,10 +17,14 @@
 #if defined(WEBRTC_VIDEO_TOOLBOX_SUPPORTED)
 
 #include <CoreMedia/CoreMedia.h>
+#include <vector>
 
 #include "webrtc/base/buffer.h"
+#include "webrtc/common_video/h264/h264_common.h"
 #include "webrtc/modules/include/module_common_types.h"
 
+using webrtc::H264::NaluIndex;
+
 namespace webrtc {
 
 // Converts a sample buffer emitted from the VideoToolbox encoder into a buffer
@@ -79,8 +83,8 @@ class AnnexBBufferReader final {
                             size_t offset) const;
 
   const uint8_t* const start_;
-  size_t offset_;
-  size_t next_offset_;
+  std::vector<NaluIndex> offsets_;
+  std::vector<NaluIndex>::iterator offset_;
   const size_t length_;
 };