Fix ThreadSafeAssociatedInterfacePtrProvider raciness.

ipc/ipc_channel_proxy.h

Index: ipc/ipc_channel_proxy.h
diff --git a/ipc/ipc_channel_proxy.h b/ipc/ipc_channel_proxy.h
index 970237fc6d30e17d098ffb432e76a3944bff9997..ade563ef6eb995e8066cb5182da8978bfcb77461 100644
--- a/ipc/ipc_channel_proxy.h
+++ b/ipc/ipc_channel_proxy.h
@@ -242,6 +242,10 @@ class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
                               context_, callback));
   }
 
+  base::SingleThreadTaskRunner* ipc_task_runner() const {
+    return context_->ipc_task_runner();
+  }
+
   // Called to clear the pointer to the IPC task runner when it's going away.
   void ClearIPCTaskRunner();