Use entities in CommonElements interface.

pkg/compiler/lib/src/js_backend/backend_helpers.dart

 // Copyright (c) 2015, 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_backend.helpers;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers, Uris;
 import '../common/resolution.dart' show Resolution;
 import '../compiler.dart' show Compiler;
@@ skipping 199 matching lines @@
       _find(jsHelperLibrary, name);
   Element _findAsyncHelper(String name) => _find(asyncLibrary, name);
   Element _findInterceptor(String name) => _find(interceptorsLibrary, name);
   Element _find(LibraryElement library, String name) {
     Element element = library.implementation.findLocal(name);
     assert(invariant(library, element != null,
         message: "Element '$name' not found in '${library.canonicalUri}'."));
     return element;
   }
 
-  Element findCoreHelper(String name) =>
-      compiler.commonElements.coreLibrary.implementation.localLookup(name);
+  Element findCoreHelper(String name) {
+    LibraryElement coreLibrary = compiler.commonElements.coreLibrary;
+    return coreLibrary.implementation.localLookup(name);
+  }
 
   ConstructorElement _findConstructor(ClassElement cls, String name) {
     cls.ensureResolved(resolution);
     ConstructorElement constructor = cls.lookupConstructor(name);
     assert(invariant(cls, constructor != null,
         message: "Constructor '$name' not found in '${cls}'."));
     return constructor;
   }
 
   void onLibraryCreated(LibraryElement library) {
@@ skipping 117 matching lines @@
     assert(loadedLibraries.containsLibrary(DART_INTERCEPTORS));
     assert(loadedLibraries.containsLibrary(DART_JS_HELPER));
 
     if (jsInvocationMirrorClass != null) {
       jsInvocationMirrorClass.ensureResolved(resolution);
       invokeOnMethod = jsInvocationMirrorClass.lookupLocalMember(INVOKE_ON);
     }
 
     // [LinkedHashMap] is reexported from dart:collection and can therefore not
     // be loaded from dart:core in [onLibraryScanned].
-    mapLiteralClass = compiler.commonElements.coreLibrary.find('LinkedHashMap');
+    LibraryElement coreLibrary = compiler.commonElements.coreLibrary;
+    mapLiteralClass = coreLibrary.find('LinkedHashMap');
     assert(invariant(
         compiler.commonElements.coreLibrary, mapLiteralClass != null,
         message: "Element 'LinkedHashMap' not found in 'dart:core'."));
 
     // TODO(kasperl): Some tests do not define the special JSArray
     // subclasses, so we check to see if they are defined before
     // trying to resolve them.
     if (jsFixedArrayClass != null) {
       jsFixedArrayClass.ensureResolved(resolution);
     }
@@ skipping 18 matching lines @@
     jsArrayClass.ensureResolved(resolution);
     jsArrayTypedConstructor = compiler.lookupElementIn(jsArrayClass, 'typed');
     jsArrayRemoveLast = compiler.lookupElementIn(jsArrayClass, 'removeLast');
     jsArrayAdd = compiler.lookupElementIn(jsArrayClass, 'add');
 
     jsStringClass.ensureResolved(resolution);
     jsStringSplit = compiler.lookupElementIn(jsStringClass, 'split');
     jsStringOperatorAdd = compiler.lookupElementIn(jsStringClass, '+');
     jsStringToString = compiler.lookupElementIn(jsStringClass, 'toString');
 
-    objectEquals = compiler.lookupElementIn(commonElements.objectClass, '==');
+    ClassElement objectClass = commonElements.objectClass;
+    objectEquals = compiler.lookupElementIn(objectClass, '==');
   }
 
   ConstructorElement _mapLiteralConstructor;
   ConstructorElement _mapLiteralConstructorEmpty;
   Element _mapLiteralUntypedMaker;
   Element _mapLiteralUntypedEmptyMaker;
 
   ConstructorElement get mapLiteralConstructor {
     _ensureMapLiteralHelpers();
     return _mapLiteralConstructor;
@@ skipping 431 matching lines @@
   }
 
   ClassElement get stackTraceClass {
     return _findHelper('_StackTrace');
   }
 
   MethodElement _objectNoSuchMethod;
 
   MethodElement get objectNoSuchMethod {
     if (_objectNoSuchMethod == null) {
-      _objectNoSuchMethod = commonElements.objectClass
-          .lookupLocalMember(Identifiers.noSuchMethod_);
+      ClassElement objectClass = commonElements.objectClass;
+      _objectNoSuchMethod =
+          objectClass.lookupLocalMember(Identifiers.noSuchMethod_);
     }
     return _objectNoSuchMethod;
   }
 
   ClassElement get constantMapClass =>
       _findHelper(JavaScriptMapConstant.DART_CLASS);
   ClassElement get constantStringMapClass =>
       _findHelper(JavaScriptMapConstant.DART_STRING_CLASS);
   ClassElement get constantProtoMapClass =>
       _findHelper(JavaScriptMapConstant.DART_PROTO_CLASS);
@@ skipping 13 matching lines @@
   }
 
   MethodElement get toStringForNativeObject {
     return _findHelper('toStringForNativeObject');
   }
 
   MethodElement get hashCodeForNativeObject {
     return _findHelper('hashCodeForNativeObject');
   }
 }