Add version-specific defines for each C interface.

ppapi/c/ppb_audio.h

 /* Copyright (c) 2011 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 PPAPI_C_PPB_AUDIO_H_
 #define PPAPI_C_PPB_AUDIO_H_
 
 #include "ppapi/c/pp_bool.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_module.h"
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/c/pp_stdint.h"
 
-#define PPB_AUDIO_INTERFACE "PPB_Audio;0.6"
+#define PPB_AUDIO_INTERFACE_0_6 "PPB_Audio;0.6"
+#define PPB_AUDIO_INTERFACE PPB_AUDIO_INTERFACE_0_6
 
 /**
  * @file
  * This file defines the PPB_Audio interface, which provides realtime stereo
  * audio streaming capabilities. Please refer to the
  * <a href="/chrome/nativeclient/docs/audio.html">Pepper Audio API Code
  * Walkthrough</a> for information on using this interface.
  */
 
 /**
@@ skipping 107 matching lines @@
    * callback completes.
    */
   PP_Bool (*StopPlayback)(PP_Resource audio);
 };
 /**
  * @}
  */
 
 #endif  /* PPAPI_C_PPB_DEVICE_CONTEXT_AUDIO_H_ */