Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/deferred_custom_element_test.dart

 // Copyright (c) 2013, 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.
 
 // Test of the graph segmentation algorithm used by deferred loading
 // to determine which elements can be deferred and which libraries
 // much be included in the initial download (loaded eagerly).
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:expect/expect.dart';
 import 'memory_compiler.dart';
 
 void main() {
   asyncTest(() async {
     CompilationResult result =
         await runCompiler(memorySourceFiles: MEMORY_SOURCE_FILES);
     Compiler compiler = result.compiler;
     var outputUnitForElement = compiler.deferredLoadTask.outputUnitForElement;
     var mainOutputUnit = compiler.deferredLoadTask.mainOutputUnit;
-    var lib =
+    dynamic lib =
         compiler.libraryLoader.lookupLibrary(Uri.parse("memory:lib.dart"));
     var customType = lib.find("CustomType");
     var foo = lib.find("foo");
     Expect.notEquals(mainOutputUnit, outputUnitForElement(foo));
     // Native elements are not deferred
     Expect.equals(mainOutputUnit, outputUnitForElement(customType));
   });
 }
 
 // The main library imports a file defining a custom element.
@@ skipping 14 matching lines @@
 var a = CustomType;
 
 class CustomType extends HtmlElement {
   factory CustomType() => null;
   CustomType.created() : super.created() ;
 }
 
 foo() {}
 """,
 };