Don't log a warning when Super Dev Mode is off.

Change-Id: Id958f469c20d283f943f85e2291b14e1238c1614
(cherry picked from commit 8ef353626aadec24e42243a35c7d82c299af17c1)
diff --git a/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeLinker.java b/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeLinker.java
index bee72ca..92a6eaa 100644
--- a/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeLinker.java
+++ b/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeLinker.java
@@ -263,7 +263,7 @@
     if (!regexp.isEmpty()) {
       return ""
           + "if (!/^" + regexp.replace("/", "\\/") + "$/.test(devModeUrl)) {\n"
-          + "  if (window.console && console.log) {\n"
+          + "  if (devModeUrl && window.console && console.log) {\n"
           + "    console.log('Ignoring non-whitelisted Dev Mode URL: ' + devModeUrl);\n"
           + "  }\n"
           + "  devModeUrl = '';"