Adds a DebugString method to QuicStreamSequencer.

net/quic/quic_stream_sequencer.cc

Index: net/quic/quic_stream_sequencer.cc
diff --git a/net/quic/quic_stream_sequencer.cc b/net/quic/quic_stream_sequencer.cc
index da26cc52fa9d4ad6470b7e6a531031a8c6563c8c..f6f0182507ba86b9e67c4d5022caac74179f424f 100644
--- a/net/quic/quic_stream_sequencer.cc
+++ b/net/quic/quic_stream_sequencer.cc
@@ -19,6 +19,7 @@
 #include "net/quic/quic_utils.h"
 #include "net/quic/reliable_quic_stream.h"
 
+using base::IntToString;
 using base::StringPiece;
 using std::min;
 using std::numeric_limits;
@@ -158,7 +159,7 @@ void QuicStreamSequencer::MarkConsumed(size_t num_bytes_consumed) {
   if (!result) {
     QUIC_BUG << "Invalid argument to MarkConsumed."
              << " expect to consume: " << num_bytes_consumed
-             << ", but not enough bytes available.";
+             << ", but not enough bytes available. " << DebugString();
     stream_->Reset(QUIC_ERROR_PROCESSING_STREAM);
     return;
   }
@@ -202,4 +203,16 @@ QuicStreamOffset QuicStreamSequencer::NumBytesConsumed() const {
   return buffered_frames_.BytesConsumed();
 }
 
+const string QuicStreamSequencer::DebugString() const {
+  // clang-format off
+  return "QuicStreamSequencer:"
+         "\n  bytes buffered: " + IntToString(NumBytesBuffered()) +
+         "\n  bytes consumed: " + IntToString( NumBytesConsumed()) +
+         "\n  has bytes to read: " +  (HasBytesToRead() ? "true" : "false") +
+         "\n  frames received: " + IntToString(num_frames_received()) +
+         "\n  close offset bytes: " + IntToString( close_offset_) +
+         "\n  is closed: " + (IsClosed() ? "true" : "false");
+  // clang-format on
+}
+
 }  // namespace net