Implement subtype relation for kernel based elements.

pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.js_emitter.program_builder;
 
 import '../../closure.dart' show ClosureTask, ClosureFieldElement;
 import '../../common.dart';
 import '../../common/names.dart' show Names, Selectors;
 import '../../constants/values.dart'
@@ skipping 10 matching lines @@
         FunctionSignature,
         GetterElement,
         LibraryElement,
         MemberElement,
         MethodElement,
         ParameterElement,
         TypedefElement,
         VariableElement;
 import '../../elements/entities.dart';
 import '../../elements/resolution_types.dart'
-    show
-        DartTypes,
-        ResolutionDartType,
-        ResolutionFunctionType,
-        ResolutionTypedefType;
-import '../../elements/types.dart' show DartType;
+    show ResolutionDartType, ResolutionFunctionType, ResolutionTypedefType;
+import '../../elements/types.dart' show DartType, DartTypes;
 import '../../js/js.dart' as js;
 import '../../js_backend/backend.dart'
     show
         RuntimeTypesChecks,
         RuntimeTypesNeed,
         RuntimeTypesEncoder,
         RuntimeTypesSubstitutions,
         SuperMemberData;
 import '../../js_backend/backend_usage.dart';
 import '../../js_backend/constant_handler_javascript.dart'
@@ skipping 1051 matching lines @@
       Constant constant = new Constant(name, holder, constantValue);
       _constants[constantValue] = constant;
     }
   }
 
   Holder _registerStaticStateHolder() {
     return _registry.registerHolder(_namer.staticStateHolder,
         isStaticStateHolder: true);
   }
 }