fix language_tests.js to use strict mode

test/codegen/language/async_throw_in_catch_test.dart

 // Copyright (c) 2015, 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.
 
 import "dart:async";
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
 class Tracer {
   final String expected;
   final String name;
   int counter = 0;
 
   Tracer(this.expected, [this.name]);
 
   void trace(msg) {
     if (name != null) {
-      print("Tracing $name: $msg");
+      //print("Tracing $name: $msg");

[vsm, 2015/08/03 20:57:33]

Maybe a comment here?   Hmm - ideally we'd have a tracing function that only
prints if the test fails.

[Jennifer Messerly, 2015/08/03 21:08:11]

Done.

     }
     Expect.equals(expected[counter], msg);
     counter++;
   }
 
   void done() {
     Expect.equals(expected.length, counter, "Received too few traces");
   }
 }
 
@@ skipping 438 matching lines @@
   await runTest("abcdefgX", foo14, "Error3");
   await runTest("abcdefg", foo15);
   await runTest("abcdfg", foo16);
   await runTest("abcdef", foo17);
   await runTest("abcde", foo18);
 }
 
 void main() {
   asyncTest(test);
 }