Throw FileSystemException from FileSystemEntity methods.

pkg/front_end/test/memory_file_system_test.dart

Index: pkg/front_end/test/memory_file_system_test.dart
diff --git a/pkg/front_end/test/memory_file_system_test.dart b/pkg/front_end/test/memory_file_system_test.dart
index 1f7d6c3f9c4c439ef545cf4849f5cfdcbc6ed7f6..139fd7082f37d8b994e6dd7c912774f5bd7f597f 100644
--- a/pkg/front_end/test/memory_file_system_test.dart
+++ b/pkg/front_end/test/memory_file_system_test.dart
@@ -8,6 +8,7 @@ library front_end.test.memory_file_system_test;
 import 'dart:convert';
 import 'dart:io' as io;
 
+import 'package:front_end/file_system.dart' show FileSystemException;
 import 'package:front_end/memory_file_system.dart';
 import 'package:path/path.dart' as pathos;
 import 'package:test/test.dart';
@@ -22,6 +23,9 @@ main() {
   });
 }
 
+const Matcher _throwsFileSystemException =
+    const Throws(const isInstanceOf<FileSystemException>());
+
 @reflectiveTest
 class FileTest extends _BaseTestNative {
   String path;
@@ -41,10 +45,36 @@ class FileTest extends _BaseTestNative {
     expect(file == entityForPath(join(tempPath, 'file.txt')), isTrue);
   }
 
+  test_exists_doesNotExist() async {
+    expect(await file.exists(), false);
+  }
+
+  test_exists_exists() async {
+    file.writeAsStringSync('x');
+    expect(await file.exists(), true);
+  }
+
   test_hashCode_samePath() {
     expect(file.hashCode, entityForPath(join(tempPath, 'file.txt')).hashCode);
   }
 
+  test_lastModified_doesNotExist() async {
+    expect(file.lastModified(), _throwsFileSystemException);
+  }
+
+  test_lastModified_increasesOnEachChange() async {
+    file.writeAsStringSync('x');
+    var mod1 = await file.lastModified();
+    file.writeAsStringSync('y');
+    var mod2 = await file.lastModified();
+    expect(mod2.isAfter(mod1), isTrue);
+
+    var file2 = entityForPath(join(tempPath, 'file2.txt'));
+    file2.writeAsStringSync('z');
+    var mod3 = await file2.lastModified();
+    expect(mod3.isAfter(mod2), isTrue);
+  }
+
   test_path() {
     expect(file.uri, context.toUri(path));
   }
@@ -57,7 +87,7 @@ class FileTest extends _BaseTestNative {
   }
 
   test_readAsBytes_doesNotExist() {
-    expect(file.readAsBytes(), throwsException);
+    expect(file.readAsBytes(), _throwsFileSystemException);
   }
 
   test_readAsBytes_exists() async {
@@ -68,11 +98,11 @@ class FileTest extends _BaseTestNative {
 
   test_readAsString_badUtf8() {
     file.writeAsBytesSync([0xc0, 0x40]); // Invalid UTF-8
-    expect(file.readAsString(), throwsException);
+    expect(file.readAsString(), _throwsFileSystemException);
   }
 
   test_readAsString_doesNotExist() {
-    expect(file.readAsString(), throwsException);
+    expect(file.readAsString(), _throwsFileSystemException);
   }
 
   test_readAsString_exists() async {
@@ -86,32 +116,6 @@ class FileTest extends _BaseTestNative {
     expect(await file.readAsString(), '\u20ac');
   }
 
-  test_exists_doesNotExist() async {
-    expect(await file.exists(), false);
-  }
-
-  test_exists_exists() async {
-    file.writeAsStringSync('x');
-    expect(await file.exists(), true);
-  }
-
-  test_lastModified_doesNotExist() async {
-    expect(file.lastModified(), throwsException);
-  }
-
-  test_lastModified_increasesOnEachChange() async {
-    file.writeAsStringSync('x');
-    var mod1 = await file.lastModified();
-    file.writeAsStringSync('y');
-    var mod2 = await file.lastModified();
-    expect(mod2.isAfter(mod1), isTrue);
-
-    var file2 = entityForPath(join(tempPath, 'file2.txt'));
-    file2.writeAsStringSync('z');
-    var mod3 = await file2.lastModified();
-    expect(mod3.isAfter(mod2), isTrue);
-  }
-
   test_writeAsBytesSync_modifyAfterRead() async {
     file.writeAsBytesSync([1]);
     (await file.readAsBytes())[0] = 2;