Make corelib_strong tests strong-mode compliant

tests/corelib_strong/iterable_skip_while_test.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.
 
 import "package:expect/expect.dart";
 
 main() {
   List<int> list1 = <int>[1, 2, 3];
   List<int> list2 = const <int>[4, 5];
   List<String> list3 = <String>[];
@@ skipping 116 matching lines @@
   Expect.isNull(it.current);
   Expect.isTrue(it.moveNext());
   Expect.isTrue(it.current != null);
   Expect.isTrue(it.moveNext());
   Expect.isTrue(it.current != null);
   Expect.isTrue(it.moveNext());
   Expect.isTrue(it.current != null);
   Expect.isFalse(it.moveNext());
   Expect.isNull(it.current);
 
-  skipWhileTrue = set2.skipWhile((x) => true);
-  it = skipWhileTrue.iterator;
-  Expect.isNull(it.current);
-  Expect.isFalse(it.moveNext());
-  Expect.isNull(it.current);
+  var dynamicSkipWhileTrue = set2.skipWhile((x) => true);
+  var dynamicIt = dynamicSkipWhileTrue.iterator;
+  Expect.isNull(dynamicIt.current);
+  Expect.isFalse(dynamicIt.moveNext());
+  Expect.isNull(dynamicIt.current);
 
-  skipWhileFalse = set2.skipWhile((x) => false);
-  it = skipWhileFalse.iterator;
-  Expect.isNull(it.current);
-  Expect.isFalse(it.moveNext());
-  Expect.isNull(it.current);
+  var dynamicSkipWhileFalse = set2.skipWhile((x) => false);
+  dynamicIt = dynamicSkipWhileFalse.iterator;
+  Expect.isNull(dynamicIt.current);
+  Expect.isFalse(dynamicIt.moveNext());
+  Expect.isNull(dynamicIt.current);
 }