do not modify globals from livecss

package.json

@@ -101,7 +101,7 @@
         "c9.ide.newresource": "#636e7a7345",
         "c9.ide.openfiles": "#2ae85a9e33",
         "c9.ide.preview": "#5f5fff0185",
-        "c9.ide.preview.browser": "#9ecfff638d",
+        "c9.ide.preview.browser": "#1de1b699c8",
         "c9.ide.preview.markdown": "#c3174d86e0",
         "c9.ide.pubsub": "#99b7289040",
         "c9.ide.readonly": "#7421caab61",

plugins/c9.preview/static/livecss.js

@@ -1016,10 +1016,12 @@ function send(message) {
         host == "local" ? "*" : host);
 }
 
-window.start = function(win) {
-    parent = win;
-    init(id);
-};
+window.addEventListener("message", function(e) {
+    if (e.data == "start-c9-livecss") {
+        parent = e.source;
+        init(id);
+    }
+});
 
 // Make sure everything is loaded
 if (parent != window)