Changed expect.dart typeAssertionsEnabled to pass strong mode tests.

pkg/expect/lib/expect.dart

 // Copyright (c) 2012, 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.
 
 /**
  * This library contains an Expect class with static methods that can be used
  * for simple unit-tests.
  */
 library expect;
 
@@ skipping 489 matching lines @@
 /// declarations to disable closed world assumptions on parameters, effectively
 /// assuming that the runtime arguments could be any value. Note that the
 /// constraints due to [TrustTypeAnnotations] still apply.
 class AssumeDynamic {
   const AssumeDynamic();
 }
 
 /// Is true iff type assertions are enabled.
 final bool typeAssertionsEnabled = (() {
   try {
-    var i = 42;
+    dynamic i = 42;
     String s = i;
   } on TypeError catch (e) {
     return true;
   }
   return false;
 })();
 
 /// Is true iff `assert` statements are enabled.
 final bool assertStatementsEnabled = (() {
   try {
     assert(false);
   } on AssertionError catch (e) {
     return true;
   }
   return false;
 })();
 
 /// Is true iff checked mode is enabled.
 final bool checkedModeEnabled =
     typeAssertionsEnabled && assertStatementsEnabled;