Move Compiler.libraries to LibraryLoader.

tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart

Index: tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
diff --git a/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart b/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
index 9e3f8af1adfa42054b6194cea5edb529b9e3662a..311e085ca47f9c1aaa06388353ed2797590ce26e 100644
--- a/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
+++ b/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
@@ -36,6 +36,10 @@ void main() {
                                    [],
                                    {});
   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);
     Expect.isNotNull(main, "Could not find 'main'");
     compiler.deferredLoadTask.onResolutionComplete(main);
@@ -46,13 +50,13 @@ void main() {
     var backend = compiler.backend;
     var classes = backend.emitter.neededClasses;
     var inputElement = classes.where((e) => e.name == 'InputElement').single;
-    var lib1 = compiler.libraries["memory:lib1.dart"];
+    var lib1 = lookupLibrary("memory:lib1.dart");
     var foo1 = lib1.find("foo1");
-    var lib2 = compiler.libraries["memory:lib2.dart"];
+    var lib2 = lookupLibrary("memory:lib2.dart");
     var foo2 = lib2.find("foo2");
-    var lib3 = compiler.libraries["memory:lib3.dart"];
+    var lib3 = lookupLibrary("memory:lib3.dart");
     var foo3 = lib3.find("foo3");
-    var lib4 = compiler.libraries["memory:lib4.dart"];
+    var lib4 = lookupLibrary("memory:lib4.dart");
     var bar1 = lib4.find("bar1");
     var bar2 = lib4.find("bar2");
     var outputClassLists = backend.emitter.outputClassLists;