Add UInt32 and UInt31 types to better infer bit operations.

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

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/js_backend/backend.dart	(revision 30666)
+++ sdk/lib/_internal/compiler/implementation/js_backend/backend.dart	(working copy)
@@ -194,6 +194,8 @@
   ClassElement jsMutableArrayClass;
   ClassElement jsFixedArrayClass;
   ClassElement jsExtendableArrayClass;
+  ClassElement jsUInt32Class;
+  ClassElement jsUInt31Class;
 
   Element jsIndexableLength;
   Element jsArrayTypedConstructor;
@@ -227,6 +229,8 @@
   TypeMask get stringType => compiler.typesTask.stringType;
   TypeMask get doubleType => compiler.typesTask.doubleType;
   TypeMask get intType => compiler.typesTask.intType;
+  TypeMask get uint32Type => compiler.typesTask.uint32Type;
+  TypeMask get uint31Type => compiler.typesTask.uint31Type;
   TypeMask get numType => compiler.typesTask.numType;
   TypeMask get boolType => compiler.typesTask.boolType;
   TypeMask get dynamicType => compiler.typesTask.dynamicType;
@@ -576,6 +580,8 @@
       // The int class must be before the double class, because the
       // emitter relies on this list for the order of type checks.
       jsIntClass = compiler.findInterceptor('JSInt'),
+      jsUInt32Class = compiler.findInterceptor('JSUInt32'),
+      jsUInt31Class = compiler.findInterceptor('JSUInt31'),
       jsDoubleClass = compiler.findInterceptor('JSDouble'),
       jsNumberClass = compiler.findInterceptor('JSNumber'),
       jsNullClass = compiler.findInterceptor('JSNull'),
@@ -847,6 +853,8 @@
       addInterceptors(jsExtendableArrayClass, enqueuer, elements);
     } else if (cls == compiler.intClass || cls == jsIntClass) {
       addInterceptors(jsIntClass, enqueuer, elements);
+      addInterceptors(jsUInt32Class, enqueuer, elements);
+      addInterceptors(jsUInt31Class, enqueuer, elements);
       addInterceptors(jsNumberClass, enqueuer, elements);
     } else if (cls == compiler.doubleClass || cls == jsDoubleClass) {
       addInterceptors(jsDoubleClass, enqueuer, elements);
@@ -857,6 +865,8 @@
       addInterceptors(jsNullClass, enqueuer, elements);
     } else if (cls == compiler.numClass || cls == jsNumberClass) {
       addInterceptors(jsIntClass, enqueuer, elements);
+      addInterceptors(jsUInt32Class, enqueuer, elements);
+      addInterceptors(jsUInt31Class, enqueuer, elements);
       addInterceptors(jsDoubleClass, enqueuer, elements);
       addInterceptors(jsNumberClass, enqueuer, elements);
     } else if (cls == jsPlainJavaScriptObjectClass) {
@@ -1415,7 +1425,8 @@
       return typeCast
           ? 'boolTypeCast'
           : 'boolTypeCheck';
-    } else if (element == jsIntClass || element == compiler.intClass) {
+    } else if (element == jsIntClass || element == compiler.intClass
+               || element == jsUInt32Class || element == jsUInt31Class) {
       if (nativeCheckOnly) return null;
       return typeCast
           ? 'intTypeCast'
@@ -1633,6 +1644,8 @@
   }
 
   ClassElement get intImplementation => jsIntClass;
+  ClassElement get uint32Implementation => jsUInt32Class;
+  ClassElement get uint31Implementation => jsUInt31Class;
   ClassElement get doubleImplementation => jsDoubleClass;
   ClassElement get numImplementation => jsNumberClass;
   ClassElement get stringImplementation => jsStringClass;