Use URIs rather than paths in front end API.

pkg/front_end/test/src/base/uri_resolver_test.dart

 // Copyright (c) 2016, 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.
 
 import 'package:front_end/src/base/uri_resolver.dart';
 import 'package:path/path.dart' as p;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(UriResolverTestNative);
     defineReflectiveTests(UriResolverTestPosix);
     defineReflectiveTests(UriResolverTestWindows);
   });
 }
 
 /// Generic URI resolver tests which do not depend on the particular path
 /// context in use.
 abstract class UriResolverTest {
   p.Context get pathContext;
 
   void test_badScheme() {
-    _expectResolution('foo:bar/baz.dart', null);
+    _expectResolutionUri('foo:bar/baz.dart', Uri.parse('foo:bar/baz.dart'));
   }
 
   void test_dart() {
     _expectResolution('dart:core', _p('sdk/lib/core/core.dart'));
     _expectResolution('dart:async', _p('sdk/lib/async/async.dart'));
   }
 
   void test_dartLeadingSlash() {
     _expectResolution('dart:/core', null);
   }
@@ skipping 12 matching lines @@
 
   void test_file() {
     _expectResolution('file:///foo.dart', _p('foo.dart'));
   }
 
   void test_fileLongPath() {
     _expectResolution('file:///foo/bar.dart', _p('foo/bar.dart'));
   }
 
   void test_noSchemeAbsolute() {
-    _expectResolution('/foo.dart', null);
+    _expectResolutionUri('/foo.dart', Uri.parse('/foo.dart'));
   }
 
   void test_noSchemeRelative() {
-    _expectResolution('foo.dart', null);
+    _expectResolution('foo.dart', 'foo.dart');
   }
 
   void test_package() {
     _expectResolution('package:foo/bar.dart', _p('packages/foo/lib/bar.dart'));
     _expectResolution('package:bar/baz.dart', _p('packages/bar/lib/baz.dart'));
   }
 
   void test_packageLeadingSlash() {
     _expectResolution('package:/foo', null);
   }
@@ skipping 23 matching lines @@
     _expectResolution('package:foo', null);
   }
 
   void test_packageUnmatchedName() {
     _expectResolution('package:doesNotExist/foo.dart', null);
   }
 
   /// Verifies that the resolution of [uriString] produces the path
   /// [expectedResult].
   void _expectResolution(String uriString, String expectedResult) {
+    _expectResolutionUri(uriString,
+        expectedResult == null ? null : pathContext.toUri(expectedResult));
+  }
+
+  /// Verifies that the resolution of [uriString] produces the URI
+  /// [expectedResult].
+  void _expectResolutionUri(String uriString, Uri expectedResult) {
     var packages = {
       'foo': _u('packages/foo/lib/'),
       'bar': _u('packages/bar/lib/')
     };
     var sdkLibraries = {
       'core': _u('sdk/lib/core/core.dart'),
       'async': _u('sdk/lib/async/async.dart')
     };
     var uriResolver = new UriResolver(packages, sdkLibraries, pathContext);
     expect(uriResolver.resolve(Uri.parse(uriString)), expectedResult);
@@ skipping 31 matching lines @@
 
   void test_fileWindowsLocal() {
     _expectResolution('file:///C:/foo/bar.dart', r'C:\foo\bar.dart');
   }
 
   void test_fileWindowsUNC() {
     _expectResolution(
         'file://computer/directory/foo.dart', r'\\computer\directory\foo.dart');
   }
 }