Replace --ppapi-keep-alive-throttle command line switch with IPC parameter.

ppapi/shared_impl/ppapi_nacl_plugin_args.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.
 
 #ifndef PPAPI_SHARED_IMPL_PPAPI_NACL_PLUGIN_ARGS_H
 #define PPAPI_SHARED_IMPL_PPAPI_NACL_PLUGIN_ARGS_H
 
 #include <string>
 #include <vector>
 
 #include "ppapi/shared_impl/ppapi_permissions.h"
 
 namespace ppapi {
 
 struct PPAPI_SHARED_EXPORT PpapiNaClPluginArgs {
  public:
   PpapiNaClPluginArgs();
   ~PpapiNaClPluginArgs();
 
   bool off_the_record;
   PpapiPermissions permissions;
   bool supports_dev_channel;
+  unsigned keepalive_throttle_interval_milliseconds;
 
   // Switches from the command-line.
   std::vector<std::string> switch_names;
   std::vector<std::string> switch_values;
 };
 
 }  // namespace ppapi
 
 #endif  // PPAPI_SHARED_IMPL_PPAPI_NACL_PLUGIN_ARGS_H