Split ppapi::PluginList from PepperPluginRegistry so that DRT could load pepper plugins.

webkit/plugins/plugin_switches.cc

Index: webkit/plugins/plugin_switches.cc
===================================================================
--- webkit/plugins/plugin_switches.cc	(revision 101488)
+++ webkit/plugins/plugin_switches.cc	(working copy)
@@ -16,6 +16,12 @@
 const char kDisablePepper3dForUntrustedUse[] =
     "disable-pepper-3d-for-untrusted-use";
 
+// Runs PPAPI (Pepper) plugins out-of-process.
+const char kPpapiOutOfProcess[]             = "ppapi-out-of-process";
+
+// Register Pepper plugins (see ppapi/plugin_registry.cc for its format).
+const char kRegisterPepperPlugins[]         = "register-pepper-plugins";
+
 #if defined(OS_WIN)
 // Used by the plugins_test when testing the older WMP plugin to force the new
 // plugin to not get loaded.