Avoid left shift of negative values when parsing H264 stream

media/filters/h264_bit_reader.cc

Index: media/filters/h264_bit_reader.cc
diff --git a/media/filters/h264_bit_reader.cc b/media/filters/h264_bit_reader.cc
index 145d2e193737fd0dd196731cb134a024e204057b..4dea4000894a1e16b827c65dd432ebefb88adbe1 100644
--- a/media/filters/h264_bit_reader.cc
+++ b/media/filters/h264_bit_reader.cc
@@ -56,7 +56,7 @@ bool H264BitReader::UpdateCurrByte() {
   --bytes_left_;
   num_remaining_bits_in_curr_byte_ = 8;
 
-  prev_two_bytes_ = (prev_two_bytes_ << 8) | curr_byte_;
+  prev_two_bytes_ = ((prev_two_bytes_ & 0xff) << 8) | curr_byte_;
 
   return true;
 }