ipc: Move AttachmentBrokerPrivileged singleton logic into ipc/.

ipc/attachment_broker_privileged.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_PRIVILEGED_H_
 #define IPC_ATTACHMENT_BROKER_PRIVILEGED_H_
 
 #include <vector>
 
 #include "base/memory/scoped_ptr.h"
 #include "ipc/attachment_broker.h"
 #include "ipc/ipc_export.h"
 
 namespace IPC {
 
 class Endpoint;
 class Sender;
 
 // This abstract subclass of AttachmentBroker is intended for use in a
 // privileged process . When unprivileged processes want to send attachments,
 // the attachments get routed through the privileged process, and more
 // specifically, an instance of this class.
 class IPC_EXPORT AttachmentBrokerPrivileged : public IPC::AttachmentBroker {
  public:
   AttachmentBrokerPrivileged();
   ~AttachmentBrokerPrivileged() override;
 
-   // On platforms that support attachment brokering, returns a new instance of
-   // a platform-specific attachment broker. Otherwise returns |nullptr|.
-   // The caller takes ownership of the newly created instance, and is
-   // responsible for ensuring that the attachment broker lives longer than
-   // every IPC::Channel. The new instance automatically registers itself as the
-   // global attachment broker.
-  static scoped_ptr<AttachmentBrokerPrivileged> CreateBroker();
+  // If there is no global attachment broker, makes a new
+  // AttachmentBrokerPrivileged and sets it as the global attachment broker.
+  // This method is thread safe.
+  static void CreateBrokerIfNeeded();
 
   // AttachmentBroker overrides.
   void RegisterCommunicationChannel(Endpoint* endpoint) override;
   void DeregisterCommunicationChannel(Endpoint* endpoint) override;
 
  protected:
   // Returns the sender whose peer's process id is |id|.
   // Returns nullptr if no sender is found.
   Sender* GetSenderWithProcessId(base::ProcessId id);
 
@@ skipping 16 matching lines @@
   void LogError(UMAError error);
 
  private:
   std::vector<Endpoint*> endpoints_;
   DISALLOW_COPY_AND_ASSIGN(AttachmentBrokerPrivileged);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_ATTACHMENT_BROKER_PRIVILEGED_H_