Fix some warnings in the core library identified by the static analyzer.

runtime/lib/mirrors_impl.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.
 
 // VM-specific implementation of the dart:mirrors library.
 
 // These values are allowed to be passed directly over the wire.
 bool isSimpleValue(var value) {
   return (value === null || value is num || value is String || value is bool);
 }
@@ skipping 32 matching lines @@
   // language objects (except for objects of type VMReference, of
   // course).
   VMReference _reference;
 }
 
 abstract class _LocalObjectMirrorImpl extends _LocalVMObjectMirrorImpl
     implements ObjectMirror {
   _LocalObjectMirrorImpl(ref) : super(ref) {}
 
   Future<InstanceMirror> invoke(String memberName,
-                                List<Object> positionalArguments,
-                                [Map<String,Object> namedArguments]) {
+                                List positionalArguments,
+                                [Map<String,Dynamic> namedArguments]) {
     if (namedArguments !== null) {
       throw new NotImplementedException('named arguments not implemented');
     }
     // Walk the arguments and make sure they are legal.
     for (int i = 0; i < positionalArguments.length; i++) {
       var arg = positionalArguments[i];
       if (arg is Mirror) {
         if (arg is! InstanceMirror) {
           throw new MirrorException(
               'positional argument $i ($arg) was not an InstanceMirror');
@@ skipping 237 matching lines @@
 
   // Creates a new local InstanceMirror
   static InstanceMirror makeLocalInstanceMirror(Object reflectee)
       native 'Mirrors_makeLocalInstanceMirror';
 
   // The IsolateMirror for the current isolate.
   static InstanceMirror mirrorOf(Object reflectee) {
     return makeLocalInstanceMirror(reflectee);
   }
 }