Introduce LibraryEntity

tests/compiler/dart2js/serialization/members_test.dart

 // Copyright (c) 2016, 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.serialization.class_members_test;
 
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/common/names.dart';
 import 'package:compiler/src/commandline_options.dart';
@@ skipping 69 matching lines @@
   class1.forEachInterfaceMember((MemberSignature member1) {
     Name name1 = member1.name;
     Name name2 = convertName(name1, compiler2);
     checkMemberSignature(class1, class2, 'interfaceMember:$name1', member1,
         class2.lookupInterfaceMember(name2));
   });
 }
 
 Name convertName(Name name, Compiler compiler) {
   if (name.isPrivate) {
-    LibraryElement library =
-        compiler.libraryLoader.lookupLibrary(name.library.canonicalUri);
-    if (!areElementsEquivalent(name.library, library)) {
-      throw 'Libraries ${name.library} and ${library} are not equivalent';
+    LibraryElement library1 = name.library;
+    LibraryElement library2 =
+        compiler.libraryLoader.lookupLibrary(library1.canonicalUri);
+    if (!areElementsEquivalent(library1, library2)) {
+      throw 'Libraries ${library1} and ${library2} are not equivalent';
     }
-    name = new Name(name.text, library, isSetter: name.isSetter);
+    name = new Name(name.text, library2, isSetter: name.isSetter);
   }
   return name;
 }
 
 void checkMember(ClassElement class1, ClassElement class2, String property,
     Member member1, Member member2) {
   if (member2 == null) {
     print('$class1 class members:');
     class1.forEachClassMember((m) => print(' ${m.name} $m'));
     print('$class2 class members:');
@@ skipping 32 matching lines @@
       areTypesEquivalent);
   check(class1, class2, '$property.functionType', member1.functionType,
       member2.functionType, areTypesEquivalent);
   check(
       class1, class2, '$property.isGetter', member1.isGetter, member2.isGetter);
   check(
       class1, class2, '$property.isSetter', member1.isSetter, member2.isSetter);
   check(
       class1, class2, '$property.isMethod', member1.isMethod, member2.isMethod);
 }