Add ClosedWorld.elementEnvironment and remove Compiler.elementEnvironment

tests/compiler/dart2js/no_such_method_enabled_test.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.
 
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/common_elements.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/elements/entities.dart';
 import 'package:compiler/src/js_backend/no_such_method_registry.dart';
@@ skipping 250 matching lines @@
       print(sources[index]);
       Compiler compiler = await results[index]();
       compiler.resolutionWorldBuilder.closeWorld();
       // Complex returns are computed during inference.
       checkTest(compiler, TESTS[index], testComplexReturns: false);
     }
   });
 }
 
 checkTest(Compiler compiler, NoSuchMethodTest test, {bool testComplexReturns}) {
-  ElementEnvironment elementEnvironment = compiler.elementEnvironment;
+  ElementEnvironment elementEnvironment =
+      compiler.frontendStrategy.elementEnvironment;
   NoSuchMethodRegistry registry = compiler.backend.noSuchMethodRegistry;
   NoSuchMethodResolver resolver = registry.internalResolverForTesting;
   FunctionEntity ObjectNSM = elementEnvironment.lookupClassMember(
-      compiler.resolution.commonElements.objectClass, 'noSuchMethod');
+      compiler.frontendStrategy.commonElements.objectClass, 'noSuchMethod');
   ClosedWorld closedWorld =
       compiler.resolutionWorldBuilder.closedWorldForTesting;
 
   // Test [NoSuchMethodResolver] results for each method.
   for (NoSuchMethodInfo info in test.methods) {
     ClassEntity cls =
         elementEnvironment.lookupClass(compiler.mainApp, info.className);
     Expect.isNotNull(cls, "Class ${info.className} not found.");
     FunctionEntity noSuchMethod =
         elementEnvironment.lookupClassMember(cls, 'noSuchMethod');
@@ skipping 59 matching lines @@
           registry.complexReturningImpls.contains(noSuchMethod),
           "Unexpected isComplexReturn result on $noSuchMethod.");
     }
   }
 
   Expect.equals(
       test.isNoSuchMethodUsed,
       closedWorld.backendUsage.isNoSuchMethodUsed,
       "Unexpected isNoSuchMethodUsed result.");
 }