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

ppapi/shared_impl/ppapi_nacl_plugin_args.cc

Index: ppapi/shared_impl/ppapi_nacl_plugin_args.cc
diff --git a/ppapi/shared_impl/ppapi_nacl_plugin_args.cc b/ppapi/shared_impl/ppapi_nacl_plugin_args.cc
index 92df690ceb3a39f4cd0fde6073d4d2ab0245fb84..4dd511040c49eb99908751c62ec1c0687023e6a6 100644
--- a/ppapi/shared_impl/ppapi_nacl_plugin_args.cc
+++ b/ppapi/shared_impl/ppapi_nacl_plugin_args.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "ppapi/shared_impl/ppapi_constants.h"
 #include "ppapi/shared_impl/ppapi_nacl_plugin_args.h"
 
 namespace ppapi {
@@ -9,7 +10,10 @@ namespace ppapi {
 // We must provide explicit definitions of these functions for builds on
 // Windows.
 PpapiNaClPluginArgs::PpapiNaClPluginArgs()
-    : off_the_record(false), supports_dev_channel(false) {}
+    : off_the_record(false),
+      supports_dev_channel(false),
+      keepalive_throttle_interval_milliseconds(
+          kKeepaliveThrottleIntervalDefaultMilliseconds) {}
 
 PpapiNaClPluginArgs::~PpapiNaClPluginArgs() {}