Media remoting: Fix bug in CastRemotingSender.

To ensure CastRemotingSender::ProcessNextInputTask is not run after
CastRemotingSender is destructed.

Bug: 820397
Change-Id: Ic97abf03fe9a264403162a51ac4458365a60efc8
Reviewed-on: https://chromium-review.googlesource.com/956750
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542241}

components/mirroring/browser/cast_remoting_sender.cc

@@ -362,7 +362,7 @@ void CastRemotingSender::OnInputTaskComplete() {
   // Always force a post task to prevent the stack from growing too deep.
   base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE, base::BindOnce(&CastRemotingSender::ProcessNextInputTask,
-                                base::Unretained(this)));
+                                weak_factory_.GetWeakPtr()));
 }
 
 void CastRemotingSender::ReadFrame(uint32_t size) {