Mojo Bindings: Fix lock-order inversion in associated controllers

mojo/public/cpp/bindings/pipe_control_message_proxy.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_PIPE_CONTROL_MESSAGE_PROXY_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_PIPE_CONTROL_MESSAGE_PROXY_H_
 
 #include "base/macros.h"
 #include "mojo/public/cpp/bindings/bindings_export.h"
 #include "mojo/public/cpp/bindings/interface_id.h"
 #include "mojo/public/cpp/bindings/lib/serialization_context.h"
 
 namespace mojo {
 
 class MessageReceiver;
 
 // Proxy for request messages defined in pipe_control_messages.mojom.
+//
+// NOTE: This object may be used from multiple threads.
 class MOJO_CPP_BINDINGS_EXPORT PipeControlMessageProxy {
  public:
-  // Doesn't take ownership of |receiver|. It must outlive this object.
+  // Doesn't take ownership of |receiver|. If This PipeControlMessageProxy will
+  // be used from multiple threads, |receiver| must be thread-safe.
   explicit PipeControlMessageProxy(MessageReceiver* receiver);
 
   void NotifyPeerEndpointClosed(InterfaceId id);
   void NotifyEndpointClosedBeforeSent(InterfaceId id);
 
  private:
   // Not owned.
   MessageReceiver* receiver_;
-  internal::SerializationContext context_;
 
   DISALLOW_COPY_AND_ASSIGN(PipeControlMessageProxy);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_PIPE_CONTROL_MESSAGE_PROXY_H_