Rewrite ExtensionApiTest.SandboxedPages to catch exceptions.

chrome/test/data/extensions/api_test/sandboxed_pages/sandboxed.html

 This page should be sandboxed.
 
 <script>
 // We're not served with the extension default CSP, we can use inline script.
 onload = function() {
   var secret = 'sandboxed_window_secret';
 
   if (chrome.extension) {
     chrome.test.notifyFail('Extension APIs should not be injected.');
     return;
   }
 
   var mainWindow = window.opener || window.top;
-  mainWindow.postMessage(mainWindow.secret, '*');
+  var mainWindowSecret = undefined;
+  try {
+    mainWindowSecret = mainWindow.secret;
+  } catch(e) {}
+  mainWindow.postMessage(mainWindowSecret, '*');
 };
 </script>