Add support for .sdkext file to analysis server

pkg/analysis_server/test/src/sdk_ext_test.dart

+// Copyright (c) 2015, 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 analysis_server.test.src.sdk_ext;
+
+import 'package:analysis_server/src/sdk_ext.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/file_system/memory_file_system.dart';
+import 'package:unittest/unittest.dart';
+
+MemoryResourceProvider resourceProvider;
+
+buildResourceProvider() {
+  resourceProvider = new MemoryResourceProvider();
+  resourceProvider.newFolder('/empty');
+  resourceProvider.newFolder('/tmp');
+  resourceProvider.newFile('/tmp/.sdkext', r'''
+  {
+    "dart:fox": "slippy.dart",
+    "dart:bear": "grizzly.dart",
+    "dart:relative": "../relative.dart",
+    "dart:deep": "deep/directory/file.dart",
+    "fart:loudly": "nomatter.dart"
+  }''');
+}
+
+clearResourceProvider() {
+  resourceProvider = null;
+}
+
+main() {
+  groupSep = ' | ';
+  group('SdkExtUriResolverTest', () {
+    setUp(() {
+      buildResourceProvider();
+    });
+    tearDown(() {
+      clearResourceProvider();
+    });
+    test('test_NullPackageMap', () {
+      var resolver = new SdkExtUriResolver(null);
+      expect(resolver.length, equals(0));
+    });
+    test('test_NoSdkExtPackageMap', () {
+      var resolver = new SdkExtUriResolver({
+        'fox': [resourceProvider.getResource('/empty')]
+      });
+      expect(resolver.length, equals(0));
+    });
+    test('test_SdkExtPackageMap', () {
+      var resolver = new SdkExtUriResolver({
+        'fox': [resourceProvider.getResource('/tmp')]
+      });
+      // We have four mappings.
+      expect(resolver.length, equals(4));
+      // Check that they map to the correct paths.
+      expect(resolver['dart:fox'], equals("/tmp/slippy.dart"));
+      expect(resolver['dart:bear'], equals("/tmp/grizzly.dart"));
+      expect(resolver['dart:relative'], equals("/relative.dart"));
+      expect(resolver['dart:deep'], equals("/tmp/deep/directory/file.dart"));
+    });
+    test('test_BadJSON', () {
+      var resolver = new SdkExtUriResolver(null);
+      resolver.addSdkExt(r'''{{{,{{}}},}}''', null);
+      expect(resolver.length, equals(0));
+    });
+  });
+}