Simplify PhysicalFileSystem implementation.

pkg/front_end/test/physical_file_system_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.
 // SharedOptions=--supermixin
 
 library front_end.test.physical_file_system_test;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io' as io;
@@ skipping 102 matching lines @@
   }
 
   test_entityForPath_normalize_dotDot() {
     expect(entityForPath(p.join(tempPath, 'foo', '..', 'file.txt')).uri,
         p.toUri(p.join(tempPath, 'file.txt')));
   }
 
   test_entityForUri() {
     expect(
         PhysicalFileSystem.instance
-            .entityForUri(Uri.parse('$tempUri/file.txt'))
+            .entityForUri(Uri.parse('${tempUri}file.txt'))
             .uri,
         p.toUri(p.join(tempPath, 'file.txt')));
   }
 
   test_entityForUri_bareUri_absolute() {
     expect(PhysicalFileSystem.instance.entityForUri(Uri.parse('/file.txt')).uri,
         p.toUri(p.fromUri('/file.txt')));
   }
 
   test_entityForUri_fileUri_relative() {
@@ skipping 18 matching lines @@
   test_entityForUri_nonFileUri() {
     expect(
         () => PhysicalFileSystem.instance
             .entityForUri(Uri.parse('package:foo/bar.dart')),
         throwsA(new isInstanceOf<Error>()));
   }
 
   test_entityForUri_normalize_dot() {
     expect(
         PhysicalFileSystem.instance
-            .entityForUri(Uri.parse('$tempUri/./file.txt'))
+            .entityForUri(Uri.parse('${tempUri}./file.txt'))
             .uri,
         p.toUri(p.join(tempPath, 'file.txt')));
   }
 
   test_entityForUri_normalize_dotDot() {
     expect(
         PhysicalFileSystem.instance
-            .entityForUri(Uri.parse('$tempUri/foo/../file.txt'))
+            .entityForUri(Uri.parse('${tempUri}foo/../file.txt'))
             .uri,
         p.toUri(p.join(tempPath, 'file.txt')));
   }
 }
 
 class _BaseTest {
   io.Directory tempDirectory;
   String tempPath;
 
   FileSystemEntity entityForPath(String path) =>
       PhysicalFileSystem.instance.entityForUri(p.toUri(path));
 
   setUp() {
     tempDirectory = io.Directory.systemTemp.createTempSync('test_file_system');
     tempPath = tempDirectory.absolute.path;
   }
 
   tearDown() async {
     try {
       tempDirectory.deleteSync(recursive: true);
     } on io.FileSystemException {
       // Sometimes on Windows the delete fails with errno 32
       // (ERROR_SHARING_VIOLATION: The process cannot access the file because it
       // is being used by another process).  Wait 1 second and try again.
       await new Future.delayed(new Duration(seconds: 1));
       tempDirectory.deleteSync(recursive: true);
     }
   }
 }