Add the "virtual" keyword on method overrides that are missing it.

chrome/plugin/npobject_proxy.cc

Index: chrome/plugin/npobject_proxy.cc
diff --git a/chrome/plugin/npobject_proxy.cc b/chrome/plugin/npobject_proxy.cc
index 26014765dae3ca0361db4a81b41c6de1c6c9d69e..f245151b62c2029903211b3ec8317de903a48487 100644
--- a/chrome/plugin/npobject_proxy.cc
+++ b/chrome/plugin/npobject_proxy.cc
@@ -46,6 +46,14 @@ NPObjectProxy* NPObjectProxy::GetProxy(NPObject* object) {
   return proxy;
 }
 
+NPObject* NPObjectProxy::GetUnderlyingNPObject() {
+  return NULL;
+}
+
+IPC::Channel::Listener* NPObjectProxy::GetChannelListener() {
+  return static_cast<IPC::Channel::Listener*>(this);
+}
+
 NPObjectProxy::NPObjectProxy(
     PluginChannelBase* channel,
     int route_id,