Add support for cross-session storage

pkg/analyzer/test/file_system/memory_file_system_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.
 
 library test.memory_file_system;
 
 import 'dart:async';
 
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
 import 'package:analyzer/src/generated/source.dart';
@@ skipping 99 matching lines @@
           provider.deleteFile(path);
           return delayed(() {
             expect(changesReceived, hasLength(1));
             expect(changesReceived[0].type, equals(ChangeType.REMOVE));
             expect(changesReceived[0].path, equals(path));
           });
         });
       });
     });
 
+    group('getStateLocation', () {
+      test('uniqueness', () {
+        String idOne = 'one';
+        Folder folderOne = provider.getStateLocation(idOne);
+        expect(folderOne, isNotNull);
+        String idTwo = 'two';
+        Folder folderTwo = provider.getStateLocation(idTwo);
+        expect(folderTwo, isNotNull);
+        expect(folderTwo, isNot(equals(folderOne)));
+        expect(provider.getStateLocation(idOne), equals(folderOne));
+      });
+    });
+
     group('newFolder', () {
       test('empty path', () {
         expect(() {
           provider.newFolder('');
         }, throwsA(new isInstanceOf<ArgumentError>()));
       });
 
       test('not absolute', () {
         expect(() {
           provider.newFolder('not/absolute');
@@ skipping 360 matching lines @@
         });
 
         test('resolveRelative', () {
           Uri relative = source.resolveRelativeUri(new Uri.file('bar/baz.dart'));
           expect(relative.path, '/foo/bar/baz.dart');
         });
       });
     });
   });
 }