Fix occasional race in VideoCapturerTrackSource seen by memcheck bot.

webrtc/pc/videocapturertracksource.cc

 /*
  *  Copyright 2012 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 364 matching lines @@
   worker_thread_->Invoke<void>(
       RTC_FROM_HERE,
       rtc::Bind(&cricket::VideoCapturer::Stop, video_capturer_.get()));
 }
 
 // OnStateChange listens to the cricket::VideoCapturer::SignalStateChange.
 void VideoCapturerTrackSource::OnStateChange(
     cricket::VideoCapturer* capturer,
     cricket::CaptureState capture_state) {
   if (rtc::Thread::Current() != signaling_thread_) {
+    // Use rtc::Unretained, because we don't want this to capture a reference
+    // to ourselves. If our destructor is called while this task is executing,
+    // that's fine; our AsyncInvoker destructor will wait for it to finish if
+    // it isn't simply canceled.
     invoker_.AsyncInvoke<void>(
         RTC_FROM_HERE, signaling_thread_,
-        rtc::Bind(&VideoCapturerTrackSource::OnStateChange, this, capturer,
-                  capture_state));
+        rtc::Bind(&VideoCapturerTrackSource::OnStateChange,
+                  rtc::Unretained(this), capturer, capture_state));
     return;
   }
 
   if (capturer == video_capturer_.get()) {
     SetState(GetReadyState(capture_state));
   }
 }
 
 }  // namespace webrtc