Mojo: Split public/cpp/system/core.h into pieces

mojo/public/cpp/system/macros.h

-// Copyright 2013 The Chromium Authors. All rights reserved.
+// Copyright 2014 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 MOJO_PUBLIC_CPP_SYSTEM_MACROS_H_
 #define MOJO_PUBLIC_CPP_SYSTEM_MACROS_H_
 
 #include "mojo/public/c/system/macros.h"
 
+// Define a set of C++ specific macros.
+// Mojo C++ API users can assume that mojo/public/cpp/system/macros.h
+// includes mojo/public/c/system/macros.h.
+
 // Annotate a virtual method indicating it must be overriding a virtual method
 // in the parent class. Use like:
 //   virtual void foo() OVERRIDE;
 #if defined(_MSC_VER) || defined(__clang__)
 #define MOJO_OVERRIDE override
 #else
 #define MOJO_OVERRIDE
 #endif
 
 // A macro to disallow the copy constructor and operator= functions.
@@ skipping 24 matching lines @@
     }; \
     type(type&); \
     void operator=(type&); \
    public: \
     operator rvalue_type() { return rvalue_type(this); } \
     type Pass() { return type(rvalue_type(this)); } \
     typedef void MoveOnlyTypeForCPP03; \
    private:
 
 #endif  // MOJO_PUBLIC_CPP_SYSTEM_MACROS_H_