Fix the issue of undefined-shift in VP8GetBit.

webrtc/modules/video_coding/utility/vp8_header_parser.cc

Index: webrtc/modules/video_coding/utility/vp8_header_parser.cc
diff --git a/webrtc/modules/video_coding/utility/vp8_header_parser.cc b/webrtc/modules/video_coding/utility/vp8_header_parser.cc
index 631385d0f25095903e676f79dc24e04ea1e1c6cd..180b555c57adaf5224eda065bb6215bc07ec5caa 100644
--- a/webrtc/modules/video_coding/utility/vp8_header_parser.cc
+++ b/webrtc/modules/video_coding/utility/vp8_header_parser.cc
@@ -7,9 +7,10 @@
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
-#include "webrtc/modules/video_coding/utility/vp8_header_parser.h"
 
+#include "webrtc/base/checks.h"
 #include "webrtc/base/logging.h"

[pbos-webrtc, 2016/04/18 15:10:14]

These should go below where they were, vp8_header_parser.h should be included
first since it belongs to this .cc file.

[jackychen_, 2016/04/18 19:18:17]

Done.

+#include "webrtc/modules/video_coding/utility/vp8_header_parser.h"
 
 namespace webrtc {
 
@@ -75,7 +76,7 @@ static int VP8GetBit(VP8BitReader* const br, int prob) {
   if (br->bits_ < 0) {
     VP8LoadNewBytes(br);
   }
-
+  RTC_CHECK_GE(br->bits_, 0);

[pbos-webrtc, 2016/04/18 15:10:14]

You can't use this for network data. We cannot crash here (which RTC_CHECK makes
us do). We need to be able to abort gracefully here.

Perhaps this function should be:

static bool VP8GetBit(VP8BitReader* br, int* out_bit, int prob), and return
true/false based on success. Then VP8LoadNewBytes should be able to pass/fail.

[jackychen_, 2016/04/18 19:18:17]

When VP8GetBit read invalid bitstream, it should pass the failure status all the
way up to GetQp to indicate the QP read for this frame is not usable. I think
your comment in patch #1 is right, the status should be a property of bitReader.
I misunderstood your comment about "abort", I thought you mean "crash", my bad!

   const int pos = br->bits_;
   const uint8_t split = (range * prob) >> 8;
   const uint8_t value = static_cast<uint8_t>(br->value_ >> pos);