Move the addition of an onError handler to earlier (onInit instead of onStart), while still support…

pkg/unittest/html_config.dart

Index: pkg/unittest/html_config.dart
===================================================================
--- pkg/unittest/html_config.dart	(revision 12649)
+++ pkg/unittest/html_config.dart	(working copy)
@@ -20,22 +20,35 @@
   // TODO(rnystrom): Get rid of this if we get canonical closures for methods.
   EventListener _onErrorClosure;
 
+  void _installErrorHandler() {
+    if (_onErrorClosure == null) {
+      _onErrorClosure =
+          (e) => handleExternalError(e, '(DOM callback has errors)');
+      // Listen for uncaught errors.
+      window.on.error.add(_onErrorClosure);
+    }
+  }
+
+  void _uninstallErrorHandler() {
+    if (_onErrorClosure != null) {
+      window.on.error.remove(_onErrorClosure);
+      _onErrorClosure = null;
+    }
+  }
+
   void onInit() {
-    _onErrorClosure =
-        (e) => handleExternalError(e, '(DOM callback has errors)');
+    _installErrorHandler();
   }
 
   void onStart() {
     window.postMessage('unittest-suite-wait-for-done', '*');
-    // Listen for uncaught errors.
-    window.on.error.add(_onErrorClosure);
   }
 
   void onTestResult(TestCase testCase) {}
 
   void onDone(int passed, int failed, int errors, List<TestCase> results,
       String uncaughtError) {
-    window.on.error.remove(_onErrorClosure);
+    _uninstallErrorHandler();
     _showResultsInPage(passed, failed, errors, results, _isLayoutTest,
         uncaughtError);
     window.postMessage('unittest-suite-done', '*');