Add runtimeType() to Object which returns canonicalized instances of Type.

lib/compiler/implementation/lib/interceptors.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.
 
 #library('dart:_interceptors');
 
 #import('coreimpl.dart');
 #import('js_helper.dart');
 
 add$1(var receiver, var value) {
@@ skipping 625 matching lines @@
   if (receiver is !int) return UNINTERCEPTED(receiver.isEven());
   return (receiver & 1) === 0;
 }
 
 isOdd(receiver) {
   if (receiver is !int) return UNINTERCEPTED(receiver.isOdd());
   return (receiver & 1) === 1;
 }
 
 get$toString(receiver) => () => toString(receiver);
+
+runtimeType(receiver) {
+  if (receiver is int) {
+    return getOrCreateCachedRuntimeType('int');
+  } else if (receiver is String) {
+    return getOrCreateCachedRuntimeType('String');
+  } else if (receiver is double) {
+    return getOrCreateCachedRuntimeType('double');
+  } else if (receiver is List) {
+    return getOrCreateCachedRuntimeType('List');
+  } else {
+    return UNINTERCEPTED(receiver.runtimeType());
+  }
+}