Do not copy expectations file to itself.

slave/skia_slave_scripts/prerender.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 """ Prepare runtime resources that are needed by Test builders but not
     Bench builders. """
 
 from build_step import BuildStep
 from utils import shell_utils
@@ skipping 115 matching lines @@
         self._device_dirs.SKImageExpectedDir())
     skimage_expected_filename = builder_name_schema.GetWaterfallBot(
         self._builder_name) + ".json"
 
     skimage_host_expectations = os.path.join(self._skimage_expected_dir,
                                              skimage_expected_filename)
 
     if os.path.exists(skimage_host_expectations):
       skimage_device_expectations = self._flavor_utils.DevicePathJoin(
           self._device_dirs.SKImageExpectedDir(), skimage_expected_filename)
-      self._flavor_utils.PushFileToDevice(skimage_host_expectations,
-          skimage_device_expectations)
+      # For builders without an attached device, PushFileToDevice will fail
+      # when attempting to copy a file to itself. In this case, there is no
+      # need to copy. Only do the push when there is an attached device,
+      # which corresponds to the case that the filepaths are equal.
+      # TODO(scroggo): Once
+      # https://code.google.com/p/skia/issues/detail?id=1571 is fixed, this
+      # check can go away.
+      if skimage_device_expectations != skimage_host_expectations:
+        self._flavor_utils.PushFileToDevice(skimage_host_expectations,
+            skimage_device_expectations)
 
     self._flavor_utils.CopyDirectoryContentsToDevice(
         self._skimage_in_dir, self._device_dirs.SKImageInDir())
 
 
     # Create a directory for the output of skimage
     self._flavor_utils.CreateCleanHostDirectory(self._skimage_out_dir)
     self._flavor_utils.CreateCleanDeviceDirectory(
         self._device_dirs.SKImageOutDir())
 
 
 if '__main__' == __name__:
   sys.exit(BuildStep.RunBuildStep(PreRender))