Add CHECK's to debug QuicStreamSequencerBuffer in weird state. Add a destruction indicator to detec…

net/quic/core/quic_stream_sequencer_buffer.h

 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_QUIC_QUIC_STREAM_SEQUENCER_BUFFER_H_
 #define NET_QUIC_QUIC_STREAM_SEQUENCER_BUFFER_H_
 
 // QuicStreamSequencerBuffer implements QuicStreamSequencerBufferInterface.
 // It is a circular stream buffer with random write and
 // in-sequence read. It consists of a vector of pointers pointing
@@ skipping 230 matching lines @@
   // such that the number of blocks never exceeds blocks_count_.
   // Each list entry can hold up to kBlockSizeBytes bytes.
   std::unique_ptr<BufferBlock* []> blocks_;
 
   // Number of bytes in buffer.
   size_t num_bytes_buffered_;
 
   // Stores all the buffered frames' start offset, length and arrival time.
   std::map<QuicStreamOffset, FrameInfo> frame_arrival_time_map_;
 
+  // For debugging use after free, assigned to 123456 in constructor and 654321
+  // in destructor. As long as it's not 123456, this means either use after free
+  // or memory corruption.
+  int32_t destruction_indicator_;
+
   DISALLOW_COPY_AND_ASSIGN(QuicStreamSequencerBuffer);
 };
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_STREAM_SEQUENCER_BUFFER_H_