Add File.lengthSync to use it for FileByteStore eviction.

pkg/analyzer/test/file_system/physical_resource_provider_test.dart

 // Copyright (c) 2014, 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.
 
 library analyzer.test.file_system.physical_resource_provider_test;
 
 import 'dart:async';
 import 'dart:core';
 import 'dart:io' as io;
 
@@ skipping 79 matching lines @@
     File file2 = PhysicalResourceProvider.INSTANCE.getResource(path);
     expect(file.hashCode, equals(file2.hashCode));
   }
 
   void test_isOrContains() {
     File file = PhysicalResourceProvider.INSTANCE.getResource(path);
     expect(file.isOrContains(path), isTrue);
     expect(file.isOrContains('foo'), isFalse);
   }
 
+  void test_lengthSync_doesNotExist() {
+    File file = PhysicalResourceProvider.INSTANCE.getResource(path);
+    expect(() {
+      file.lengthSync;
+    }, throwsA(_isFileSystemException));
+  }
+
+  void test_lengthSync_exists() {
+    List<int> bytes = <int>[1, 2, 3, 4, 5];
+    new io.File(path).writeAsBytesSync(bytes);
+    expect(file.lengthSync, bytes.length);
+  }
+
   void test_modificationStamp_doesNotExist() {
     File file = PhysicalResourceProvider.INSTANCE.getResource(path);
     expect(() {
       file.modificationStamp;
     }, throwsA(_isFileSystemException));
   }
 
   void test_modificationStamp_exists() {
     new io.File(path).writeAsStringSync('contents');
     File file = PhysicalResourceProvider.INSTANCE.getResource(path);
@@ skipping 513 matching lines @@
 
   setUp() {
     tempDirectory = io.Directory.systemTemp.createTempSync('test_resource');
     tempPath = tempDirectory.absolute.path;
   }
 
   tearDown() {
     tempDirectory.deleteSync(recursive: true);
   }
 }