Disable Super Dev Mode in web workers

There are linkers that subclass CrossSiteIFrameLinker but run in
environments where 'window' is undefined. Don't include the
Super Dev Mode hook, since it assumes 'window'.

Change-Id: I5d381fc29ca1738068fa5b8f259dd1ac4ed65221
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 39f4eea..bee72ca 100644
--- a/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeLinker.java
+++ b/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeLinker.java
@@ -236,6 +236,11 @@
    * (May return either the JavaScript itself or the name of a Java resource ending with ".js".)
    */
   protected String getJsDevModeRedirectHook(LinkerContext context) {
+    if (shouldUseSelfForWindowAndDocument(context)) {
+      // Probably a Web Worker. Super Dev Mode isn't supported.
+      return "";
+    }
+
     // Enable Super Dev Mode for this app if the devModeRedirectEnabled config property is true.
     if (getBooleanConfigurationProperty(context, "devModeRedirectEnabled", true)) {
       return "com/google/gwt/core/linker/DevModeRedirectHook.js";