Use macros to define pepper interfaces

ppapi/thunk/interfaces_preamble.h

Index: ppapi/thunk/interfaces_preamble.h
diff --git a/ppapi/thunk/interfaces_preamble.h b/ppapi/thunk/interfaces_preamble.h
new file mode 100644
index 0000000000000000000000000000000000000000..7fe1d77bbf820eb913f4c14912f68a7be9664b7d
--- /dev/null
+++ b/ppapi/thunk/interfaces_preamble.h
@@ -0,0 +1,31 @@
+// 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.
+
+// This file defines empty versions of the macros used in the interfaces_*.h
+// files, as long as they aren't already defined. This allows users of those
+// files to only implement the macros they need, and everything else will
+// compile.
+//
+// Include this file at the top, and interfaces_postamble.h at the bottom. The
+// postamble will clean up these definitions.
+
+#ifndef PROXIED_API
+#define PROXIED_API(api_name)
+#define UNDEFINE_PROXIED_API
+#endif
+
+#ifndef UNPROXIED_API
+#define UNPROXIED_API(api_name)
+#define UNDEFINE_UNPROXIED_API
+#endif
+
+#ifndef PROXIED_IFACE
+#define PROXIED_IFACE(api_name, iface_str, iface_struct)
+#define UNDEFINE_PROXIED_IFACE
+#endif
+
+#ifndef UNPROXIED_IFACE
+#define UNPROXIED_IFACE(api_name, iface_str, iface_struct)
+#define UNDEFINE_UNPROXIED_IFACE
+#endif