Change MirrorSystem.libraries to Map<Uri, String>

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 61a1e656598eae7c84382714d9490e42efbe8a39..15074767d69159a58aaf5fd5702d22d83a6292b3 100644
--- a/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
+++ b/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
@@ -17,7 +17,7 @@ import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
        as dart2js;
 
 import '../../../sdk/lib/_internal/compiler/implementation/filenames.dart'
-       show getCurrentDirectory, nativeToUriPath;
+       show currentDirectory, nativeToUriPath;
 
 import '../../../sdk/lib/_internal/compiler/implementation/source_file.dart'
        show SourceFile;
@@ -41,8 +41,7 @@ class MemorySourceFileProvider extends SourceFileProvider {
 }
 
 void main() {
-  Uri cwd = getCurrentDirectory();
-  Uri script = cwd.resolve(nativeToUriPath(new Options().script));
+  Uri script = currentDirectory.resolve(nativeToUriPath(new Options().script));
   Uri libraryRoot = script.resolve('../../../sdk/');
   Uri packageRoot = script.resolve('./packages/');