Fix an attachment broker race condition.

ipc/attachment_broker.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 IPC_ATTACHMENT_BROKER_H_
 #define IPC_ATTACHMENT_BROKER_H_
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
@@ skipping 89 matching lines @@
   virtual void RegisterCommunicationChannel(
       Endpoint* endpoint,
       scoped_refptr<base::SingleThreadTaskRunner> runner);
   virtual void DeregisterCommunicationChannel(Endpoint* endpoint);
 
   // In each unprivileged process, exactly one channel should be used to
   // communicate brokerable attachments with the broker process.
   virtual void RegisterBrokerCommunicationChannel(Endpoint* endpoint);
   virtual void DeregisterBrokerCommunicationChannel(Endpoint* endpoint);
 
+  // Informs the attachment broker that a channel endpoint has received its
+  // peer's PID.
+  virtual void ReceivedPeerPid(base::ProcessId peer_pid);
+
   // True if and only if this broker is privileged.
   virtual bool IsPrivilegedBroker();
 
  protected:
   using AttachmentVector = std::vector<scoped_refptr<BrokerableAttachment>>;
 
   // Adds |attachment| to |attachments_|, and notifies the observers.
   void HandleReceivedAttachment(
       const scoped_refptr<BrokerableAttachment>& attachment);
 
@@ skipping 43 matching lines @@
 
   // The AttachmentBroker can be accessed from any thread, so modifications to
   // internal state must be guarded by a lock.
   base::Lock lock_;
   DISALLOW_COPY_AND_ASSIGN(AttachmentBroker);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_ATTACHMENT_BROKER_H_