Move ScopedIPCSupport into its own build rule.

ipc/mojo/scoped_ipc_support.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_MOJO_SCOPED_IPC_SUPPORT_H_
 #define IPC_MOJO_SCOPED_IPC_SUPPORT_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/task_runner.h"
-#include "ipc/ipc_export.h"
 
 namespace IPC {
 
 // Performs any necessary Mojo IPC initialization on construction, and shuts
 // down Mojo IPC on destruction.
 //
 // This should be instantiated once per process and retained as long as Mojo IPC
 // is needed. The TaskRunner passed to the constructor should outlive this
 // object.
-class IPC_MOJO_EXPORT ScopedIPCSupport {
+class ScopedIPCSupport {
  public:
   ScopedIPCSupport(scoped_refptr<base::TaskRunner> io_thread_task_runner);
   ~ScopedIPCSupport();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ScopedIPCSupport);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_MOJO_SCOPED_IPC_SUPPORT_H_