ipc: Use a global for the process's attachment broker.

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/process/process_handle.h"
@@ skipping 32 matching lines @@
 class IPC_EXPORT AttachmentBroker : public Listener {
  public:
   // A standard observer interface that allows consumers of the AttachmentBroker
   // to be notified when a new attachment has been received.
   class Observer {
    public:
     virtual void ReceivedBrokerableAttachmentWithId(
         const BrokerableAttachment::AttachmentId& id) = 0;
   };
 
+  // Each process has at most one attachment broker. The process is responsible
+  // for ensuring that |broker| stays alive for the life time of the process.

[Tom Sepez, 2015/09/11 15:58:30]

nit: lifetime

[erikchen, 2015/09/11 20:16:02]

I updated the comment to say:
"""
Each process has at most one attachment broker. The process is responsible
for ensuring that |broker| stays alive for as long as the process is
sending/receiving ipc messages.
"""

+  static void SetGlobal(AttachmentBroker* broker);
+  static AttachmentBroker* GetGlobal();
+
   AttachmentBroker();
   ~AttachmentBroker() override;
 
   // Sends |attachment| to |destination_process|. The implementation uses an
   // IPC::Channel to communicate with the broker process. This may be the same
   // IPC::Channel that is requesting the brokering of an attachment.
   // Returns true on success and false otherwise.
   virtual bool SendAttachmentToProcess(const BrokerableAttachment* attachment,
                                        base::ProcessId destination_process) = 0;
 
@@ skipping 34 matching lines @@
   // better performance.
   AttachmentVector attachments_;
 
   std::vector<Observer*> observers_;
   DISALLOW_COPY_AND_ASSIGN(AttachmentBroker);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_ATTACHMENT_BROKER_H_