Enable extension APIs for content scripts.

chrome/test/data/extensions/api_test/content_scripts/extension_iframe/iframe.html

 <script>
 // Simple success test: we want content-script APIs to be available (like
 // sendRequest), but other APIs to be undefined.
 var success = false;
 
 try {
-  var foo = chrome.tabs;
+  var foo = chrome.tabs.create;
 } catch (e) {
   success = e.message.indexOf(
       " can only be used in extension processes.") > -1;
 }
 
 chrome.extension.sendRequest({success: success});
 </script>