Provide a Mojo equivalent of ThreadSafeSender.

ipc/ipc_channel_proxy.cc

Index: ipc/ipc_channel_proxy.cc
diff --git a/ipc/ipc_channel_proxy.cc b/ipc/ipc_channel_proxy.cc
index 3365aef248747a657965bfd82c5751a8e69630b8..8928520a150e7662fe02abd433b19e957a169068 100644
--- a/ipc/ipc_channel_proxy.cc
+++ b/ipc/ipc_channel_proxy.cc
@@ -311,6 +311,11 @@ void ChannelProxy::Context::OnRemoveFilter(MessageFilter* filter) {
   NOTREACHED() << "filter to be removed not found";
 }
 
+void ChannelProxy::Context::RunWithChannel(
+    const RunOnIOThreadCallback& callback) {
+  callback.Run(channel_.get());
+}
+
 // Called on the listener's thread
 void ChannelProxy::Context::AddFilter(MessageFilter* filter) {
   base::AutoLock auto_lock(pending_filters_lock_);
@@ -610,6 +615,12 @@ void ChannelProxy::GetGenericRemoteAssociatedInterface(
                             context_, name, base::Passed(&handle)));
 }
 
+void ChannelProxy::RunOnIOThread(const RunOnIOThreadCallback& callback) {
+  DCHECK(did_init_);
+  context_->ipc_task_runner()->PostTask(
+      FROM_HERE, base::Bind(&Context::RunWithChannel, context_, callback));
+}
+
 void ChannelProxy::ClearIPCTaskRunner() {
   DCHECK(CalledOnValidThread());