Fix most implementations of UriResolver.restoreAbsolute.

pkg/analyzer/test/generated/all_the_rest_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 engine.all_the_rest_test;
 
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analyzer/src/generated/ast.dart' hide ConstantEvaluator;
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 7953 matching lines @@
     expect(result.fullName,
         FileUtilities2.createFile("/does/not/exist.dart").getAbsolutePath());
   }
 
   void test_resolve_nonFile() {
     UriResolver resolver = new FileUriResolver();
     Source result =
         resolver.resolveAbsolute(parseUriWithException("dart:core"));
     expect(result, isNull);
   }
+
+  void test_restore() {
+    UriResolver resolver = new FileUriResolver();
+    Uri uri = parseUriWithException('file:///foo/bar.dart');
+    Source source = resolver.resolveAbsolute(uri);
+    expect(source, isNotNull);
+    expect(resolver.restoreAbsolute(source), uri);
+    expect(
+        resolver.restoreAbsolute(
+            new NonExistingSource(source.fullName, null, null)),
+        uri);
+  }
 }
 
 @reflectiveTest
 class HtmlParserTest extends EngineTestCase {
   /**
    * The name of the 'script' tag in an HTML file.
    */
   static String _TAG_SCRIPT = "script";
   void fail_parse_scriptWithComment() {
     String scriptBody = r'''
@@ skipping 1002 matching lines @@
     if (_expectedExternalScriptName == null) {
       expect(scriptSource, isNull, reason: "script $scriptIndex");
     } else {
       expect(scriptSource, isNotNull, reason: "script $scriptIndex");
       String actualExternalScriptName = scriptSource.shortName;
       expect(actualExternalScriptName, _expectedExternalScriptName,
           reason: "script $scriptIndex");
     }
   }
 }