Add file.filesizes to recipe engine core modules.

recipe_modules/file/examples/copytree.py

 # Copyright 2017 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 DEPS = [
   "file",
   "path",
 ]
 
 
 def RunSteps(api):
   file_names = ['a', 'aa', 'b', 'bb', 'c', 'cc']
 
   dest = api.path['start_dir'].join('some dir')
   api.file.ensure_directory('ensure "some dir"', dest)
   for fname in file_names:
     api.file.write_text('write %s' % fname, dest.join(fname), fname)
+  api.file.filesizes('check filesizes', *file_names)
 
   dest2 = api.path['start_dir'].join('some other dir')
   api.file.rmtree('make sure dest is gone', dest2)
   api.file.copytree('copy it', dest, dest2)
 
   paths = api.file.listdir('list new dir', dest2, file_names)
   assert paths == [dest2.join(n) for n in file_names], paths
 
   paths = api.file.glob_paths('glob *a', dest2, '*a', ['a', 'aa'])
   assert paths == [dest2.join('a'), dest2.join('aa')], paths
@@ skipping 10 matching lines @@
   assert paths == [dest2.join(p) for p in ['aa', 'c', 'cc']], paths
 
   api.file.rmcontents('remove "some other dir/*"', dest2)
   assert api.path.exists(dest2), dest2
 
 
 
 def GenTests(api):
   yield api.test('basic')