Change TypeMask.base to be a ClassElement.

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

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index b2cd1d9abf6fd552e386964c28d20149a760aa0d..4fd399c2ae02358e75d1aacf873489e4cf3e478d 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -660,17 +660,17 @@ class JavaScriptBackend extends Backend {
     validateInterceptorImplementsAllObjectMethods(jsInterceptorClass);
 
     stringType = new HBoundedType(
-        new TypeMask.nonNullExact(jsStringClass.rawType));
+        new TypeMask.nonNullExact(jsStringClass));
     indexablePrimitiveType = new HBoundedType(
-        new TypeMask.nonNullSubtype(jsIndexableClass.rawType));
+        new TypeMask.nonNullSubtype(jsIndexableClass));
     readableArrayType = new HBoundedType(
-        new TypeMask.nonNullSubclass(jsArrayClass.rawType));
+        new TypeMask.nonNullSubclass(jsArrayClass));
     mutableArrayType = new HBoundedType(
-        new TypeMask.nonNullSubclass(jsMutableArrayClass.rawType));
+        new TypeMask.nonNullSubclass(jsMutableArrayClass));
     fixedArrayType = new HBoundedType(
-        new TypeMask.nonNullExact(jsFixedArrayClass.rawType));
+        new TypeMask.nonNullExact(jsFixedArrayClass));
     extendableArrayType = new HBoundedType(
-        new TypeMask.nonNullExact(jsExtendableArrayClass.rawType));
+        new TypeMask.nonNullExact(jsExtendableArrayClass));
   }
 
   void validateInterceptorImplementsAllObjectMethods(