Fix Browser Controller to not reuse iFrames, which can sometimes cause bad state to be left between…

tools/testing/dart/browser_controller.dart

Index: tools/testing/dart/browser_controller.dart
diff --git a/tools/testing/dart/browser_controller.dart b/tools/testing/dart/browser_controller.dart
index 92166e4f788b424211354f59806752045cd20ca5..d98933180c60e0df173b54f0fbad5d2d3f5ec867 100644
--- a/tools/testing/dart/browser_controller.dart
+++ b/tools/testing/dart/browser_controller.dart
@@ -1374,13 +1374,18 @@ class BrowserTestingServer {
         number_div.innerHTML = number_of_tests;
         executing_div.innerHTML = url;
         if (use_iframe) {
+          var embedded_iframe = document.getElementById('embedded_iframe');
+          embedded_iframe.parentNode.removeChild(embedded_iframe);
+
+          embedded_iframe = document.createElement('iframe');
+          embedded_iframe.id = 'embedded_iframe';
+          document.body.appendChild(embedded_iframe);
           embedded_iframe.src = url;
         } else {
-          if (testing_window == undefined) {
-            testing_window = window.open(url);
-          } else {
-            testing_window.location = url;
+          if (typeof testing_window != 'undefined') {
+            testing_window.close();
           }
+          testing_window = window.open(url);
         }
       }