Add UInt32 and UInt31 types to better infer bit operations.

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

Index: sdk/lib/_internal/compiler/implementation/types/types.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/types/types.dart	(revision 30666)
+++ sdk/lib/_internal/compiler/implementation/types/types.dart	(working copy)
@@ -53,8 +53,11 @@
   }
 
   TypeMask dynamicTypeCache;
+  TypeMask nonNullTypeCache;
   TypeMask nullTypeCache;
   TypeMask intTypeCache;
+  TypeMask uint32TypeCache;
+  TypeMask uint31TypeCache;
   TypeMask doubleTypeCache;
   TypeMask numTypeCache;
   TypeMask boolTypeCache;
@@ -75,14 +78,37 @@
     return dynamicTypeCache;
   }
 
+  TypeMask get nonNullType {
+    if (nonNullTypeCache == null) {
+      nonNullTypeCache = new TypeMask.nonNullSubclass(compiler.objectClass);
+    }
+    return nonNullTypeCache;
+  }
+
   TypeMask get intType {
     if (intTypeCache == null) {
-      intTypeCache = new TypeMask.nonNullExact(
+      intTypeCache = new TypeMask.nonNullSubclass(
           compiler.backend.intImplementation);
     }
     return intTypeCache;
   }
 
+  TypeMask get uint32Type {
+    if (uint32TypeCache == null) {
+      uint32TypeCache = new TypeMask.nonNullSubclass(
+          compiler.backend.uint32Implementation);
+    }
+    return uint32TypeCache;
+  }
+
+  TypeMask get uint31Type {
+    if (uint31TypeCache == null) {
+      uint31TypeCache = new TypeMask.nonNullExact(
+          compiler.backend.uint31Implementation);
+    }
+    return uint31TypeCache;
+  }
+
   TypeMask get doubleType {
     if (doubleTypeCache == null) {
       doubleTypeCache = new TypeMask.nonNullExact(