Further reduce use of Element in codegen.

pkg/compiler/lib/src/elements/entities.dart

Index: pkg/compiler/lib/src/elements/entities.dart
diff --git a/pkg/compiler/lib/src/elements/entities.dart b/pkg/compiler/lib/src/elements/entities.dart
index f46c790603819198d8bb5e3677cff4f72fd4af02..c7942686970011a70dbed104d97a808ae5493d10 100644
--- a/pkg/compiler/lib/src/elements/entities.dart
+++ b/pkg/compiler/lib/src/elements/entities.dart
@@ -12,8 +12,6 @@ import 'elements.dart' show Entity;
 /// and/or Dart-in-JS classes.
 abstract class ClassEntity extends Entity {
   bool get isClosure;
-  void forEachInstanceField(f(ClassEntity cls, FieldEntity field),
-      {bool includeSuperAndInjectedMembers: false});
 }
 
 abstract class TypeVariableEntity extends Entity {
@@ -27,6 +25,7 @@ abstract class TypeVariableEntity extends Entity {
 /// Currently only [MemberElement] but later also kernel based Dart members
 /// and/or Dart-in-JS properties.
 abstract class MemberEntity extends Entity {
+  bool get isConstructor;
   bool get isField;
   bool get isFunction;
   bool get isGetter;