Fix #19137: handle when regexp doesn't match in constructorNameFallback

tests/html/websocket_test.dart

 library WebSocketTest;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_individual_config.dart';
 import 'dart:html';
 
 main() {
 
   useHtmlIndividualConfiguration();
 
   group('supported', () {
@@ skipping 17 matching lines @@
     if (WebSocket.supported) {
       test('echo', () {
         var socket = new WebSocket('ws://${window.location.host}/ws');
 
         socket.onOpen.first.then((_) {
           socket.send('hello!');
         });
 
         return socket.onMessage.first.then((MessageEvent e) {
           expect(e.data, 'hello!');
+          socket.close();
+        });
+      });
+
+      test('regression for 19137', () {
+        // The server supports ws, but not wss, this will yield an error that we
+        // expect to catch below.
+        var socket = new WebSocket('wss://${window.location.host}/ws');
+        socket.onOpen.first.then((_) => socket.send('hello!'));
+        return socket.onError.first.then((e) {
+          // This test is modeled after a comment in issue #19137. We haven't
+          // verified that this is the casue, but the theory is that on Safari
+          // we will reach this point correctly, we then try to get an
+          // interceptor for `e` to call `.toString` on it, but our
+          // get-interceptor logic crashes.  This is because the process of
+          // finding the interceptor may ask to extract the constructor name,
+          // and that code assumes that the name matches a specific regular
+          // expression.  Apparently that regular expression doesn't match on
+          // Safari 7 and the line below would ends up throwing and error of the
+          // form:
+          //
+          //   TypeError: null is not an object (evaluating
+          //     'String(a.constructor).match(/^\s*function\s*([\w$]*)\s*\(/)')
+          //     at ...
+          //
+          print('$e was caught');
+          socket.close();
         });
       });
     }
   });
 }