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

ppapi/proxy/plugin_globals.h

Index: ppapi/proxy/plugin_globals.h
diff --git a/ppapi/proxy/plugin_globals.h b/ppapi/proxy/plugin_globals.h
index dac33b613fe52c3e94c0627896c847cb611ddf7c..5dc614d239bd72f24e84a11b9fd8290f72facdf8 100644
--- a/ppapi/proxy/plugin_globals.h
+++ b/ppapi/proxy/plugin_globals.h
@@ -137,8 +137,7 @@ class PPAPI_PROXY_EXPORT PluginGlobals : public PpapiGlobals {
   // Interval to limit how many IPC messages are sent indicating that the plugin
   // is active and should be kept alive. The value must be smaller than any
   // threshold used to kill inactive plugins by the embedder host.
-  int keepalive_throttle_interval_milliseconds() const;
-  void set_keepalive_throttle_interval_milliseconds(int i);
+  void set_keepalive_throttle_interval_milliseconds(unsigned i);
 
  private:
   class BrowserSender;
@@ -183,7 +182,7 @@ class PPAPI_PROXY_EXPORT PluginGlobals : public PpapiGlobals {
   // all considered active.
   bool plugin_recently_active_;
 
-  int keepalive_throttle_interval_milliseconds_;
+  unsigned keepalive_throttle_interval_milliseconds_;
 
   // Member variables should appear before the WeakPtrFactory, see weak_ptr.h.
   base::WeakPtrFactory<PluginGlobals> weak_factory_;