IPC: Fix attachment brokering race condition.

ipc/ipc_channel.h

 // Copyright (c) 2012 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 IPC_IPC_CHANNEL_H_
 #define IPC_IPC_CHANNEL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 148 matching lines @@
       const IPC::ChannelHandle& channel_handle,
       Listener* listener);
 
   ~Channel() override;
 
   // Connect the pipe.  On the server side, this will initiate
   // waiting for connections.  On the client, it attempts to
   // connect to a pre-existing pipe.  Note, calling Connect()
   // will not block the calling thread and may complete
   // asynchronously.
+  //
+  // The subclass implementation must call WillConnect() at the beginning of its
+  // implementation.
   virtual bool Connect() WARN_UNUSED_RESULT = 0;
 
   // Close this Channel explicitly.  May be called multiple times.
   // On POSIX calling close on an IPC channel that listens for connections will
   // cause it to close any accepted connections, and it will stop listening for
   // new connections. If you just want to close the currently accepted
   // connection and listen for new ones, use ResetToAcceptingConnectionState.
   virtual void Close() = 0;
 
   // Get its own process id. This value is told to the peer.
@@ skipping 70 matching lines @@
     ~OutputElement();
     size_t size() const { return message_ ? message_->size() : length_; }
     const void* data() const { return message_ ? message_->data() : buffer_; }
     Message* get_message() const { return message_.get(); }
 
    private:
     std::unique_ptr<Message> message_;
     void* buffer_;
     size_t length_;
   };
+
+  // Endpoint overrides.
+  void OnSetAttachmentBrokerEndpoint() override;
+
+  // Subclasses must call this method at the beginning of their implementation
+  // of Connect().
+  void WillConnect();
+
+ private:
+  bool did_start_connect_ = false;
 };
 
 #if defined(OS_POSIX)
 // SocketPair() creates a pair of socket FDs suitable for using with
 // IPC::Channel.
 IPC_EXPORT bool SocketPair(int* fd1, int* fd2);
 #endif
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_CHANNEL_H_