[mojo-edk] Ensure there is only one ProcessIncomingMessages() task posted to the IO thread.

mojo/edk/system/node_controller.h

 // Copyright 2016 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_EDK_SYSTEM_NODE_CONTROLLER_H_
 #define MOJO_EDK_SYSTEM_NODE_CONTROLLER_H_
 
 #include <memory>
 #include <queue>
 #include <unordered_map>
@@ skipping 257 matching lines @@
   // The name of our broker node, if any.
   ports::NodeName broker_name_;
 
   // A queue of pending child names waiting to be connected to a broker.
   std::queue<ports::NodeName> pending_broker_clients_;
 
   // Messages waiting to be relayed by the broker once it's known.
   std::unordered_map<ports::NodeName, OutgoingMessageQueue>
       pending_relay_messages_;
 
-  // Guards |incoming_messages_|.
+  // Guards |incoming_messages_| and |incoming_messages_task_posted_|.
   base::Lock messages_lock_;
   std::queue<ports::ScopedMessage> incoming_messages_;
+  // Ensures that there is only one incoming messages task posted to the IO
+  // thread.
+  bool incoming_messages_task_posted_ = false;
   // Flag to fast-path checking |incoming_messages_|.
   AtomicFlag incoming_messages_flag_;
 
   // Guards |shutdown_callback_|.
   base::Lock shutdown_lock_;
 
   // Set by RequestShutdown(). If this is non-null, the controller will
   // begin polling the Node to see if clean shutdown is possible any time the
   // Node's state is modified by the controller.
   base::Closure shutdown_callback_;
@@ skipping 21 matching lines @@
   std::unique_ptr<MachPortRelay> mach_port_relay_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(NodeController);
 };
 
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_NODE_CONTROLLER_H_