Move Compiler.libraries to LibraryLoader.

tests/compiler/dart2js/metadata_test.dart

 // Copyright (c) 2012, 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:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 import 'package:compiler/implementation/dart2jslib.dart'
     show PrimitiveConstant;
@@ skipping 145 matching lines @@
 
     Uri async = new Uri(scheme: 'dart', path: 'async');
 
     var compiler = compilerFor(source, uri)
         ..registerSource(partUri, partSource)
         ..registerSource(libUri, libSource)
         ..registerSource(async, 'class DeferredLibrary {}');
 
     asyncTest(() => compiler.runCompiler(uri).then((_) {
       compiler.enqueuer.resolution.queueIsClosed = false;
-      LibraryElement element = compiler.libraries['$uri'];
+      LibraryElement element = compiler.libraryLoader.lookupLibrary(uri);
       Expect.isNotNull(element, 'Cannot find $uri');
 
       Link<MetadataAnnotation> metadata = extractMetadata(element);
       Expect.equals(1, length(metadata));
 
       PartialMetadataAnnotation annotation = metadata.head;
       annotation.ensureResolved(compiler);
       PrimitiveConstant value = annotation.value;
       Expect.stringEquals('xyz', value.value.slowToString());
 
@@ skipping 34 matching lines @@
   compileAndCheckLibrary(source,
                          (e) => e.compilationUnits.first.partTag.metadata);
 }
 
 void main() {
   testClassMetadata();
   testTopLevelMethodMetadata();
   testTopLevelFieldMetadata();
   testLibraryTags();
 }