Bug 930458 - Add missing includes for gcc 4.5 compatibility. r=ehsan

dom/plugins/test/testplugin/nptest_gtk2.cpp

@@ -45,6 +45,7 @@
 #include <gtk/gtk.h>
 #include <unistd.h>
 
+#include "mozilla/NullPtr.h"
 #include "mozilla/IntentionalCrash.h"
 
  using namespace std;

dom/plugins/test/testplugin/nptest_utils.cpp

@@ -33,6 +33,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>
+#include "mozilla/NullPtr.h"
 
 NPUTF8*
 createCStringFromNPVariant(const NPVariant* variant)