Avoid double task trampoline for Pipeline state transitions.

media/filters/chunk_demuxer.cc

Index: media/filters/chunk_demuxer.cc
diff --git a/media/filters/chunk_demuxer.cc b/media/filters/chunk_demuxer.cc
index 1b57c3a1b18d35587bf6f07e8b2f6a68c258f15f..92761805200fb94ecdae19372577b730420314f0 100644
--- a/media/filters/chunk_demuxer.cc
+++ b/media/filters/chunk_demuxer.cc
@@ -1132,7 +1132,9 @@ void ChunkDemuxer::Initialize(
 
   base::AutoLock auto_lock(lock_);
 
+  // Always post the callback because |this| could be destroyed upon failure.
   init_cb_ = BindToCurrentLoop(cb);
+
   if (state_ == SHUTDOWN) {
     base::ResetAndReturn(&init_cb_).Run(DEMUXER_ERROR_COULD_NOT_OPEN);
     return;