Move Compiler.libraries to LibraryLoader.

tests/compiler/dart2js/deferred_not_in_main_test.dart

 // Copyright (c) 2014, 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.
 
 // Test of the graph segmentation algorithm used by deferred loading
 // to determine which elements can be deferred and which libraries
 // much be included in the initial download (loaded eagerly).
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
@@ skipping 18 matching lines @@
   var handler = new FormattingDiagnosticHandler(provider);
 
   Compiler compiler = new Compiler(provider.readStringFromUri,
                                    (name, extension) => new FakeOutputStream(),
                                    handler.diagnosticHandler,
                                    libraryRoot,
                                    packageRoot,
                                    [],
                                    {});
   asyncTest(() => compiler.run(Uri.parse('memory:main.dart')).then((_) {
+    lookupLibrary(name) {
+      return compiler.libraryLoader.lookupLibrary(Uri.parse(name));
+    }
+
     var main = compiler.mainApp.find(dart2js.Compiler.MAIN);
     var outputUnitForElement = compiler.deferredLoadTask.outputUnitForElement;
 
     var mainOutputUnit = compiler.deferredLoadTask.mainOutputUnit;
     var backend = compiler.backend;
     var classes = backend.emitter.neededClasses;
-    var lib1 = compiler.libraries["memory:lib1.dart"];
-    var lib2 = compiler.libraries["memory:lib2.dart"];
+    var lib1 = lookupLibrary("memory:lib1.dart");
+    var lib2 = lookupLibrary("memory:lib2.dart");
     var foo1 = lib1.find("foo1");
     var foo2 = lib2.find("foo2");
 
     var outputClassLists = backend.emitter.outputClassLists;
 
     Expect.notEquals(mainOutputUnit, outputUnitForElement(foo2));
   }));
 }
 
 // lib1 imports lib2 deferred. But mainlib never uses DeferredLibrary.
@@ skipping 19 matching lines @@
 void foo1() {
   def.load().then((_) => lib2.foo2());
 }
 """,
   "lib2.dart":"""
 library lib2;
 
 void foo2() {}
 """,
 };