Further reduce use of Element in codegen.

pkg/compiler/lib/src/types/masks.dart

Index: pkg/compiler/lib/src/types/masks.dart
diff --git a/pkg/compiler/lib/src/types/masks.dart b/pkg/compiler/lib/src/types/masks.dart
index a713dc8acb4ac2e5c7825578c79b6ed385b2f72b..01dff0200bf509a9447d3fabf6c144ae5ad58ee9 100644
--- a/pkg/compiler/lib/src/types/masks.dart
+++ b/pkg/compiler/lib/src/types/masks.dart
@@ -197,4 +197,12 @@ class CommonMasks {
                 closedWorld.backendClasses.indexingBehaviorImplementation,
                 closedWorld));
   }
+
+  TypeMask createNonNullExact(ClassElement cls) {
+    return new TypeMask.nonNullExact(cls.declaration, closedWorld);
+  }
+
+  TypeMask createNonNullSubtype(ClassElement cls) {
+    return new TypeMask.nonNullSubtype(cls.declaration, closedWorld);
+  }
 }