Let IPC::SyncMessageFilter take advantage of thread-safe Send.

content/child/child_thread_impl.cc

Index: content/child/child_thread_impl.cc
diff --git a/content/child/child_thread_impl.cc b/content/child/child_thread_impl.cc
index b0b7dd413de91ef89845930cc94a72104e0e24ff..3978af0b74a438b49b1758b62803fa11f0f28ca1 100644
--- a/content/child/child_thread_impl.cc
+++ b/content/child/child_thread_impl.cc
@@ -366,8 +366,7 @@ void ChildThreadImpl::Init(const Options& options) {
 
   mojo_application_.reset(new MojoApplication(GetIOTaskRunner()));
 
-  sync_message_filter_ =
-      new IPC::SyncMessageFilter(ChildProcess::current()->GetShutDownEvent());
+  sync_message_filter_ = channel_->CreateSyncMessageFilter();
   thread_safe_sender_ = new ThreadSafeSender(
       message_loop_->task_runner(), sync_message_filter_.get());
 
@@ -394,7 +393,6 @@ void ChildThreadImpl::Init(const Options& options) {
   push_dispatcher_ = new PushDispatcher(thread_safe_sender_.get());
 
   channel_->AddFilter(histogram_message_filter_.get());
-  channel_->AddFilter(sync_message_filter_.get());
   channel_->AddFilter(resource_message_filter_.get());
   channel_->AddFilter(quota_message_filter_->GetFilter());
   channel_->AddFilter(notification_dispatcher_->GetFilter());