Reference a bug in a comment for a disabled data channel test.

webrtc/api/peerconnectionendtoend_unittest.cc

 /*
  *  Copyright 2013 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 383 matching lines @@
 }
 #endif  // HAVE_QUIC
 
 // Verifies that a DataChannel added from an OPEN message functions after
 // a channel has been previously closed (webrtc issue 3778).
 // This previously failed because the new channel re-uses the ID of the closed
 // channel, and the closed channel was incorrectly still assigned to the id.
 // TODO(deadbeef): This is disabled because there's currently a race condition
 // caused by the fact that a data channel signals that it's closed before it
 // really is. Re-enable this test once that's fixed.
+// See: https://bugs.chromium.org/p/webrtc/issues/detail?id=4453
 TEST_F(PeerConnectionEndToEndTest,
        DISABLED_DataChannelFromOpenWorksAfterClose) {
   MAYBE_SKIP_TEST(rtc::SSLStreamAdapter::HaveDtlsSrtp);
 
   CreatePcs();
 
   webrtc::DataChannelInit init;
   rtc::scoped_refptr<DataChannelInterface> caller_dc(
       caller_->CreateDataChannel("data", init));
 
@@ skipping 31 matching lines @@
   WaitForDataChannelsToOpen(caller_dc, callee_signaled_data_channels_, 0);
   // This removes the reference to the remote data channel that we hold.
   callee_signaled_data_channels_.clear();
   caller_dc->Close();
   EXPECT_EQ_WAIT(DataChannelInterface::kClosed, caller_dc->state(), kMaxWait);
 
   // Wait for a bit longer so the remote data channel will receive the
   // close message and be destroyed.
   rtc::Thread::Current()->ProcessMessages(100);
 }