Add ClosedWorld.elementEnvironment and remove Compiler.elementEnvironment

tests/compiler/dart2js/inference/inference_test_helper.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.
 
 import 'package:compiler/src/common.dart';
 import 'package:compiler/src/common_elements.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/elements/entities.dart';
 import 'package:compiler/src/resolution/tree_elements.dart';
@@ skipping 28 matching lines @@
       });
     } else if (member.isTypedef) {
       // Skip.
     } else {
       checkMember(compiler, expectedMap, member);
     }
   });
   expectedMap.forEach((Id id, String expected) {
     reportHere(
         compiler.reporter,
-        computeSpannable(compiler.elementEnvironment, mainUri, id),
+        computeSpannable(compiler.resolution.elementEnvironment, mainUri, id),
         'expected:${expected},actual:null');
   });
   Expect.isTrue(expectedMap.isEmpty, "Ids not found: $expectedMap.");
 }
 
 void checkMemberAstTypeMasks(
     Compiler compiler, Map<Id, String> expectedMap, MemberElement member) {
   ResolvedAst resolvedAst = member.resolvedAst;
   if (resolvedAst.kind != ResolvedAstKind.PARSED) return;
   compiler.reporter.withCurrentElement(member.implementation, () {
@@ skipping 113 matching lines @@
   visitSend(Send node) {
     checkSend(node);
     visitNode(node);
   }
 
   visitSendSet(SendSet node) {
     checkSend(node);
     visitNode(node);
   }
 }