Add File.lengthSync to use it for FileByteStore eviction.

pkg/analyzer/lib/file_system/physical_file_system.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.file_system.physical_file_system;
 
 import 'dart:async';
 import 'dart:core';
 import 'dart:io' as io;
 
@@ skipping 109 matching lines @@
 /**
  * A `dart:io` based implementation of [File].
  */
 class _PhysicalFile extends _PhysicalResource implements File {
   _PhysicalFile(io.File file) : super(file);
 
   @override
   Stream<WatchEvent> get changes => new FileWatcher(_entry.path).events;
 
   @override
+  int get lengthSync {
+    try {
+      return _file.lengthSync();
+    } on io.FileSystemException catch (exception) {
+      throw new FileSystemException(exception.path, exception.message);
+    }
+  }
+
+  @override
   int get modificationStamp {
     try {
       return _file.lastModifiedSync().millisecondsSinceEpoch;
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
   }
 
   /**
    * Return the underlying file being represented by this wrapper.
@@ skipping 264 matching lines @@
           timer.cancel();
         }
       });
       return completer.future;
     }
     _isSpawning = true;
     _runner = await IsolateRunner.spawn();
     return _runner;
   }
 }