Add file.filesizes to recipe engine core modules.

recipe_modules/file/example.disable

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from recipe_engine.types import freeze
 
 DEPS = [
   'depot_tools/infra_paths',
   'file',
   'recipe_engine/path',
@@ skipping 16 matching lines @@
 def RunSteps(api):
   # listdir demo.
   result = api.file.listdir('fake dir', '/fake/dir')
   for element in result:
     api.step('manipulate %s' % str(element), ['some', 'command'])
 
   result = api.file.listdir('other', '/faker/dir')
   for element in result:
     api.step('manipulate %s' % str(element), ['some', 'command'])
 
+  # filesizes demo.
+  filepaths = ['/fake/one', '/fake/other']
+  sizes = api.file.filesizes('filesizes', filepaths)
+  for f, s in zip(filepaths, sizes):
+    api.step('filesize of %s is %d bytes' % (f, s))
+
   # mkdtemp demo.
   for prefix in ('prefix_a', 'prefix_b'):
     # Create temp dir.
     temp_dir = api.path.mkdtemp(prefix)
     assert api.path.exists(temp_dir)
     # Make |temp_dir| surface in expectation files.
     api.step('print %s' % prefix, ['echo', temp_dir])
 
   # move demo
   api.file.move(
@@ skipping 38 matching lines @@
         'glob', tmp_dir.join('*'),
         test_data=[tmp_dir.join('dummy_file')])
     assert files == [tmp_dir.join('dummy_file')], files
 
   finally:
     api.file.rmtree('cleanup', tmp_dir)
     api.file.rmtree('cleanup2', new_tmp)
 
 
 def GenTests(api):
-  yield api.test('file_io') + api.file.listdir('other', ['aaa'])
-
+  yield (api.test('file_io')
+         + api.file.listdir('other', ['aaa'])
+         + api.file.filesizes([1, 44]))