Fix Windows path handling in uri_resolver_test.

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() {
@@ skipping 28 matching lines @@
 
   void test_dartLeadingSlash3() {
     _expectResolution('dart:///core', null);
   }
 
   void test_dartPart() {
     _expectResolution('dart:core/bool.dart', _p('sdk/lib/core/bool.dart'));
   }
 
   void test_file() {
-    _expectResolution('file:///foo.dart', _p('foo.dart'));
+    _expectResolution(_fileUri('foo.dart'), _p('foo.dart'));
   }
 
   void test_fileLongPath() {
-    _expectResolution('file:///foo/bar.dart', _p('foo/bar.dart'));
+    _expectResolution(_fileUri('foo/bar.dart'), _p('foo/bar.dart'));
   }
 
   void test_noSchemeAbsolute() {
     _expectResolutionUri('/foo.dart', Uri.parse('/foo.dart'));
   }
 
   void test_noSchemeRelative() {
     _expectResolution('foo.dart', 'foo.dart');
   }
 
@@ skipping 50 matching lines @@
       '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);
     expect(uriResolver.resolve(Uri.parse(uriString)), expectedResult);
   }
 
+  /// Prepends "file:///", plus a Windows drive letter if applicable, to the
+  /// given path.
+  String _fileUri(String pathPart) {
+    if (pathContext.separator == '/') {
+      return 'file:///$pathPart';
+    } else {
+      return 'file:///C:/$pathPart';
+    }
+  }
+
   /// Converts a posix style path into a path appropriate for the current path
   /// context.
   String _p(String posixPath) {
-    return pathContext.fromUri(_u(posixPath));
+    if (!posixPath.startsWith('/')) posixPath = '/$posixPath';
+    if (pathContext.separator == '/') return posixPath;
+    // Windows
+    return 'C:${posixPath.replaceAll('/', pathContext.separator)}';
   }
 
   /// Converts a posix style path into a file URI.
-  Uri _u(String posixPath) => Uri.parse('file:///$posixPath');
+  Uri _u(String posixPath) => pathContext.toUri(_p(posixPath));
 }
 
 /// Override of [UriResolverTest] which uses the native path context for the
 /// platform the test is running on.
 @reflectiveTest
 class UriResolverTestNative extends UriResolverTest {
   final p.Context pathContext = p.context;
 }
 
 /// Override of [UriResolverTest] which uses a posix path context, regardless of
@@ skipping 11 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');
   }
 }