Add MOJO_{BEGIN,END}_EXTERN_C macros, and use them.

mojo/public/c/system/message_pipe.h

 // 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.
 
 // This file contains types/constants and functions specific to message pipes.
 //
 // Note: This header should be compilable as C.
 
 #ifndef MOJO_PUBLIC_C_SYSTEM_MESSAGE_PIPE_H_
 #define MOJO_PUBLIC_C_SYSTEM_MESSAGE_PIPE_H_
@@ skipping 36 matching lines @@
 //   |MOJO_READ_MESSAGE_FLAG_NONE| - No flags; default mode.
 //   |MOJO_READ_MESSAGE_FLAG_MAY_DISCARD| - If the message is unable to be read
 //       for whatever reason (e.g., the caller-supplied buffer is too small),
 //       discard the message (i.e., simply dequeue it).
 
 typedef uint32_t MojoReadMessageFlags;
 
 #define MOJO_READ_MESSAGE_FLAG_NONE ((MojoReadMessageFlags)0)
 #define MOJO_READ_MESSAGE_FLAG_MAY_DISCARD ((MojoReadMessageFlags)1 << 0)
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+MOJO_BEGIN_EXTERN_C
 
 // Creates a message pipe, which is a bidirectional communication channel for
 // framed data (i.e., messages). Messages can contain plain data and/or Mojo
 // handles.
 //
 // |options| may be set to null for a message pipe with the default options.
 //
 // On success, |*message_pipe_handle0| and |*message_pipe_handle1| are set to
 // handles for the two endpoints (ports) for the message pipe.
 //
@@ skipping 74 matching lines @@
 //
 // TODO(vtl): Reconsider the |MOJO_RESULT_RESOURCE_EXHAUSTED| error code; should
 // distinguish this from the hitting-system-limits case.
 MojoResult MojoReadMessage(MojoHandle message_pipe_handle,
                            void* bytes,            // Optional out.
                            uint32_t* num_bytes,    // Optional in/out.
                            MojoHandle* handles,    // Optional out.
                            uint32_t* num_handles,  // Optional in/out.
                            MojoReadMessageFlags flags);
 
-#ifdef __cplusplus
-}  // extern "C"
-#endif
+MOJO_END_EXTERN_C
 
 #endif  // MOJO_PUBLIC_C_SYSTEM_MESSAGE_PIPE_H_