Cap the memory usage in FFMpegDemuxer.

media/base/decoder_buffer_queue.h

Index: media/base/decoder_buffer_queue.h
diff --git a/media/base/decoder_buffer_queue.h b/media/base/decoder_buffer_queue.h
index 938db63123e5523135bfcd529907114a3799c908..9c2c2dc7b19d14fed06f2f20c052fd14cd828e9f 100644
--- a/media/base/decoder_buffer_queue.h
+++ b/media/base/decoder_buffer_queue.h
@@ -51,6 +51,9 @@ class MEDIA_EXPORT DecoderBufferQueue {
   // Returns zero if the queue is empty.
   base::TimeDelta Duration();
 
+  // Returns the total size of buffers inside the queue.
+  size_t data_size() const { return data_size_; }
+
  private:
   typedef std::deque<scoped_refptr<DecoderBuffer> > Queue;
   Queue queue_;
@@ -62,6 +65,9 @@ class MEDIA_EXPORT DecoderBufferQueue {
 
   base::TimeDelta earliest_valid_timestamp_;
 
+  // Total size in bytes of buffers in the queue.
+  size_t data_size_;
+
   DISALLOW_COPY_AND_ASSIGN(DecoderBufferQueue);
 };