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

chrome/plugin/npobject_stub.cc

Index: chrome/plugin/npobject_stub.cc
diff --git a/chrome/plugin/npobject_stub.cc b/chrome/plugin/npobject_stub.cc
index 18e5b4cad7cbf456c194afa2d63ecdf00a641723..c7117561ababeb2bdb04ec20404ccfc5436efc07 100644
--- a/chrome/plugin/npobject_stub.cc
+++ b/chrome/plugin/npobject_stub.cc
@@ -54,6 +54,14 @@ void NPObjectStub::OnPluginDestroyed() {
   MessageLoop::current()->DeleteSoon(FROM_HERE, this);
 }
 
+NPObject* NPObjectStub::GetUnderlyingNPObject() {
+  return npobject_;
+}
+
+IPC::Channel::Listener* NPObjectStub::GetChannelListener() {
+  return static_cast<IPC::Channel::Listener*>(this);
+}
+
 void NPObjectStub::OnMessageReceived(const IPC::Message& msg) {
   child_process_logging::SetActiveURL(page_url_);