Fix file.copy recipe_module to not fail if files are already equal.

scripts/slave/recipe_modules/file/api.py

 # 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 import recipe_api
 
 
 class FileApi(recipe_api.RecipeApi):
   """FileApi contains helper functions for reading and writing files."""
 
   def __init__(self, **kwargs):
     super(FileApi, self).__init__(**kwargs)
 
   def copy(self, name, source, dest, step_test_data=None, **kwargs):
     """Copy a file."""
     return self.m.python.inline(
         name,
         """
         import shutil
         import sys

[Michael Achenbach, 2016/10/07 09:05:28]

nit: Since this script's getting more complex it could be converted into a
resource to prevent expectation drama in the future.

+        # Apparently, shutil.copy fails if files are binary-equal on *nix OSes.
+        # See http://crbug.com/636168#c8.
+        if hasattr(shutil, '_samefile'):
+          if shutil._samefile(sys.argv[1], sys.argv[2]):
+            sys.exit(0)
         shutil.copy(sys.argv[1], sys.argv[2])
         """,
         args=[source, dest],
         add_python_log=False,
         step_test_data=step_test_data,
         **kwargs
     )
 
   def copytree(self, name, source, dest, symlinks=False, **kwargs):
     """Run shutil.copytree in a step."""
@@ skipping 179 matching lines @@
     self.m.python.inline(
       'rmwildcard %s in %s' % (pattern, path),
       """
       import sys
       from common import chromium_utils # Error? See https://crbug.com/584783.
 
       chromium_utils.RemoveFilesWildcards(sys.argv[1], root=sys.argv[2])
       """,
       args=[pattern,path],
       **kwargs)