Simplify PhysicalFileSystem implementation.

pkg/front_end/test/physical_file_system_test.dart

Index: pkg/front_end/test/physical_file_system_test.dart
diff --git a/pkg/front_end/test/physical_file_system_test.dart b/pkg/front_end/test/physical_file_system_test.dart
index 2a8cbb6377b99bdb81620fa5435c3cd15df5c5bc..c3a2ef195a5819176487aded68f657262bf71288 100644
--- a/pkg/front_end/test/physical_file_system_test.dart
+++ b/pkg/front_end/test/physical_file_system_test.dart
@@ -120,7 +120,7 @@ class PhysicalFileSystemTest extends _BaseTest {
   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')));
   }
@@ -159,7 +159,7 @@ class PhysicalFileSystemTest extends _BaseTest {
   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')));
   }
@@ -167,7 +167,7 @@ class PhysicalFileSystemTest extends _BaseTest {
   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')));
   }