Added sanity check to VCMDecodingState::UsingFlexibleMode to prevent OOB error.

webrtc/modules/video_coding/decoding_state.cc

 /*
  *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 273 matching lines @@
     }
   }
   return true;
 }
 
 bool VCMDecodingState::UsingPictureId(const VCMFrameBuffer* frame) const {
   return (frame->PictureId() != kNoPictureId && picture_id_ != kNoPictureId);
 }
 
 bool VCMDecodingState::UsingFlexibleMode(const VCMFrameBuffer* frame) const {
-  return frame->CodecSpecific()->codecType == kVideoCodecVP9 &&
-         frame->CodecSpecific()->codecSpecific.VP9.flexible_mode;
+  bool is_flexible_mode =
+      frame->CodecSpecific()->codecType == kVideoCodecVP9 &&
+      frame->CodecSpecific()->codecSpecific.VP9.flexible_mode;
+  if (is_flexible_mode && frame->PictureId() == kNoPictureId) {
+    LOG(LS_WARNING) << "Frame is marked as using flexible mode but no"
+                    << "picture id is set.";
+    return false;
+  }
+  return is_flexible_mode;
 }
 
 // TODO(philipel): change how check work, this check practially
 // limits the max p_diff to 64.
 bool VCMDecodingState::AheadOfFramesDecodedClearedTo(uint16_t index) const {
   // No way of knowing for sure if we are actually ahead of
   // frame_decoded_cleared_to_. We just make the assumption
   // that we are not trying to reference back to a very old
   // index, but instead are referencing a newer index.
   uint16_t diff =
@@ skipping 44 matching lines @@
           return false;
         }
         break;
       }
     }
   }
   return true;
 }
 
 }  // namespace webrtc