Add UInt32 and UInt31 types to better infer bit operations.

sdk/lib/_internal/compiler/implementation/compiler.dart

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/compiler.dart	(revision 30666)
+++ sdk/lib/_internal/compiler/implementation/compiler.dart	(working copy)
@@ -254,6 +254,8 @@
   ClassElement get typeImplementation => compiler.typeClass;
   ClassElement get boolImplementation => compiler.boolClass;
   ClassElement get nullImplementation => compiler.nullClass;
+  ClassElement get uint32Implementation => compiler.intClass;
+  ClassElement get uint31Implementation => compiler.intClass;
 
   ClassElement defaultSuperclass(ClassElement element) => compiler.objectClass;
 
@@ -263,6 +265,8 @@
     return classElement == compiler.objectClass;
   }
 
+  bool isInterceptorClass(ClassElement element) => false;
+
   void registerStaticUse(Element element, Enqueuer enqueuer) {}
 
   Future onLibraryLoaded(LibraryElement library, Uri uri) {