Split KernelToElementMap into sub-interfaces

pkg/compiler/lib/src/js_model/js_strategy.dart

 // Copyright (c) 2017, 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_model.strategy;
 
 import '../closure.dart' show ClosureConversionTask;
 import '../common/tasks.dart';
 import '../common_elements.dart';
 import '../compiler.dart';
@@ skipping 18 matching lines @@
 import '../universe/world_builder.dart';
 import '../util/emptyset.dart';
 import '../world.dart';
 import 'elements.dart';
 
 class JsBackendStrategy implements KernelBackendStrategy {
   final Compiler _compiler;
   final JsToFrontendMap _map = new JsToFrontendMapImpl();
   ElementEnvironment _elementEnvironment;
   CommonElements _commonElements;
-  KernelToElementMap _elementMap;
+  KernelToElementMapForBuilding _elementMap;
   ClosureConversionTask _closureDataLookup;
   final GlobalLocalsMap _globalLocalsMap = new GlobalLocalsMap();
 
   JsBackendStrategy(this._compiler);
 
-  KernelToElementMap get elementMap {
+  KernelToElementMapForBuilding get elementMap {
     if (_elementMap == null) {
       KernelFrontEndStrategy strategy = _compiler.frontendStrategy;
-      KernelToElementMap elementMap = strategy.elementMap;
+      KernelToElementMapForBuilding elementMap = strategy.elementMap;
       _elementMap = new JsKernelToElementMap(
           _map, _elementEnvironment, _commonElements, elementMap);
     }
     return _elementMap;
   }
 
   GlobalLocalsMap get globalLocalsMapForTesting => _globalLocalsMap;
 
   @override
   ClosedWorldRefiner createClosedWorldRefiner(ClosedWorld closedWorld) {
@@ skipping 98 matching lines @@
       ClosedWorld closedWorld,
       SelectorConstraintsStrategy selectorConstraintsStrategy) {
     return new KernelCodegenWorldBuilder(
         elementMap,
         closedWorld.elementEnvironment,
         nativeBasicData,
         closedWorld,
         selectorConstraintsStrategy);
   }
 }