Cloning a bunch of stuff from the native_client repository at r6528

ppapi/native_client/src/shared/ppapi_proxy/completion_callback.srpc

+# Copyright (c) 2010 The Native Client Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# RPC method that supports invocation of plugin-side callbacks from the browser.
+{
+ 'name': 'CompletionCallbackRpc',
+ 'rpcs': [
+          {'name': 'RunCompletionCallback',
+           'inputs': [['callback_id', 'int32_t'],
+                      ['result', 'int32_t'],
+                      ['read_buffer', 'char[]' ],
+                     ],
+           'outputs': []
+          },
+         ]
+}