some fixes for --strong warnings

lib/src/utils.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.
 
 /// Holds a couple utility functions used at various places in the system.
 library dev_compiler.src.utils;
 
 import 'dart:io';
 
 import 'package:path/path.dart' as path;
@@ skipping 364 matching lines @@
 bool inInvocationContext(SimpleIdentifier node) {
   var parent = node.parent;
   return parent is MethodInvocation && parent.methodName == node;
 }
 
 // TODO(vsm): Move this onto the appropriate class.  Ideally, we'd attach
 // it to TypeProvider.
 
 final _objectMap = new Expando('providerToObjectMap');
 Map<String, DartType> getObjectMemberMap(TypeProvider typeProvider) {
-  Map<String, DartType> map = _objectMap[typeProvider];
+  var map = _objectMap[typeProvider] as Map<String, DartType>;
   if (map == null) {
     map = <String, DartType>{};
     _objectMap[typeProvider] = map;
     var objectType = typeProvider.objectType;
     var element = objectType.element;
     // Only record methods (including getters) with no parameters.  As parameters are contravariant wrt
     // type, using Object's version may be too strict.
     // Add instance methods.
     element.methods.where((method) => !method.isStatic).forEach((method) {
       map[method.name] = method.type;
@@ skipping 49 matching lines @@
   } else {
     // TODO(jmesserly): this is for backwards compat, but not sure it's very
     // useful to log this.
     return 'AnalyzerMessage';
   }
 }
 
 bool isInlineJS(Element e) => e is FunctionElement &&
     e.library.source.uri.toString() == 'dart:_foreign_helper' &&
     e.name == 'JS';