Test scripts: Detect and report error in accessing window.parent in browser_controller.

tools/testing/dart/test_controller.js

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /*
  * The communication protocol between test_controller.js and the driving
  * page are JSON encoded messages of the following form:
  *   message = {
  *      is_first_message: true/false,
  *      is_status_update: true/false,
@@ skipping 91 matching lines @@
   notifyDone('FAIL');
 };
 
 // testRunner is provided by content shell.
 // It is not available in browser tests.
 var testRunner = window.testRunner || window.layoutTestController;
 var isContentShell = testRunner;
 
 var waitForDone = false;
 
+var driverWindowCached = false;
+var driverWindow;
+var reportingDriverWindowError = false;
+
 // Returns the driving window object if available
+// This function occasionally returns null instead of the
+// parent on Android content shell, so we cache the value
+// to get a consistent answer.
 function getDriverWindow() {
   if (window != window.parent) {
     // We're running in an iframe.
-    return window.parent;
+    result = window.parent;
   } else if (window.opener) {
     // We were opened by another window.
-    return window.opener;
+    result = window.opener;
+  } else {
+    result = null;
   }
-  return null;
+  if (driverWindowCached) {
+    if (result != driverWindow) {
+      recordEvent('debug', 'Driver windows changed: was null == ' +
+           (driverWindow == null) + ', is null == ' + (result == null));
+      // notifyDone calls back into this function multiple times.  Avoid loop.
+      if (!reportingDriverWindowError) {

[ricow1, 2014/08/14 15:24:10]

I assume this is to get us to fail explicitly to debug this?

+        reportingDriverWindowError = true;
+        notifyDone('FAIL');
+      }
+    }
+  } else {
+    driverWindowCached = true;
+    driverWindow = result;
+  }
+  return driverWindow;
 }
 
 function usingBrowserController() {
   return getDriverWindow() != null;
 }
 
 function buildDomEvent() {
   return {
       type: 'dom',
       value: '' + window.document.documentElement.innerHTML,
@@ skipping 154 matching lines @@
   dartPrint('dart-calling-main');
   try {
     main();
   } catch (e) {
     recordEvent('sync_exception', 'Exception: ' + e + '\nStack: ' + e.stack);
     notifyDone('FAIL');
     return;
   }
   dartPrint('dart-main-done');
 }