Avoid overflow in checking for emulation bytes in rbsp.

webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc

Index: webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc
diff --git a/webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc b/webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc
index 034e761dcd4d30177d86982f47e5c8ce28508c68..9f76ccf646e5f6fe918608f94fdc6525355082f9 100644
--- a/webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc
+++ b/webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc
@@ -36,7 +36,7 @@ bool H264SpsParser::Parse() {
   // section 7.3.1 of the H.264 standard.
   rtc::ByteBuffer rbsp_buffer;
   for (size_t i = 0; i < byte_length_;) {
-    if (i + 3 < byte_length_ && sps_[i] == 0 && sps_[i + 1] == 0 &&
+    if (byte_length_ - i >= 3 && sps_[i] == 0 && sps_[i + 1] == 0 &&

[pbos-webrtc, 2015/07/09 09:20:07]

Can you put a comment here saying that we check (byte_length_ - i) since i <
byte_length_ there's no risk of overflow? Since we're doing specific things here
to avoid overflow it'd be nice to state them so that it doesn't look like it's
just written in a different style.

         sps_[i + 2] == 3) {
       // Two rbsp bytes + the emulation byte.
       rbsp_buffer.WriteBytes(sps_bytes + i, 2);