Have ExtensionHost use TabContents instead of RenderViewHost. Try #2. The first

chrome/browser/extensions/extension_webkit_preferences.h

Index: chrome/browser/extensions/extension_webkit_preferences.h
diff --git a/chrome/browser/extensions/extension_webkit_preferences.h b/chrome/browser/extensions/extension_webkit_preferences.h
index 508e8a85868bbb6fca43ddd9ad673276f2fc0f80..e035294984808a591989465e33eb9fd57046cd6e 100644
--- a/chrome/browser/extensions/extension_webkit_preferences.h
+++ b/chrome/browser/extensions/extension_webkit_preferences.h
@@ -5,12 +5,16 @@
 #ifndef CHROME_BROWSER_EXTENSIONS_EXTENSION_WEBKIT_PREFERENCES_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_WEBKIT_PREFERENCES_H_
 
+#include "chrome/common/chrome_view_types.h"
+
 class Extension;
 struct WebPreferences;
 
 namespace extension_webkit_preferences {
 
-void SetPreferences(WebPreferences* preferences, const Extension* extension);
+void SetPreferences(const Extension* extension,
+                    content::ViewType render_view_type,
+                    WebPreferences* webkit_prefs);
 
 }  // namespace extension_webkit_preferences