Introduce git merge driver for the blink reformatting

gclient.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.
 
 """Meta checkout manager supporting both Subversion and GIT."""
 # Files
 #   .gclient      : Current client configuration, written by 'config' command.
 #                   Format is a Python script defining 'solutions', a list whose
 #                   entries each are maps binding the strings "name" and "url"
@@ skipping 865 matching lines @@
           continue
         prefix = os.path.commonprefix(
             [self.root.root_dir.lower(), file_list[i].lower()])
         file_list[i] = file_list[i][len(prefix):]
         # Strip any leading path separators.
         while file_list[i].startswith(('\\', '/')):
           file_list[i] = file_list[i][1:]
 
     # Always parse the DEPS file.
     self.ParseDepsFile()
+
+    # Setup the merge driver for The Great Blink Reformatting. This does just
+    # setup a custom merge-driver in the git config of the Chromium main project
+    # but does not have any effect until somebody changes the .gitattributes
+    # to refer to it. See crbug.com/574611 for more.
+    # TODO(primiano): remove some weeks after the reformatting. ETA: Oct 2016.
+    if parsed_url == CHROMIUM_SRC_URL:
+      CFG_PREFIX = 'merge.clang_format_merge_driver'
+      try:
+        merge_driver = self._used_scm._Capture(
+            ['config', CFG_PREFIX + '.driver']).strip()
+      except subprocess2.CalledProcessError:
+        merge_driver = None
+
+      if not merge_driver:
+        print('Installing clang-format merge driver for crbug/574611')
+        self._used_scm._Capture(['config', CFG_PREFIX + '.name',
+                                 'clang-format merge driver (crbug/574611)'])
+        self._used_scm._Capture(['config', CFG_PREFIX + '.driver',
+                                 'clang_format_merge_driver %O %A %B %L %P'])
+        self._used_scm._Capture(['config', CFG_PREFIX + '.recursive', 'binary'])
+
     self._run_is_done(file_list or [], parsed_url)
     if command in ('update', 'revert') and not options.noprehooks:
       self.RunPreDepsHooks()
 
     if self.recursion_limit:
       # Parse the dependencies of this dependency.
       for s in self.dependencies:
         work_queue.enqueue(s)
 
     if command == 'recurse':
@@ skipping 1478 matching lines @@
 
 
 if '__main__' == __name__:
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)
 
 # vim: ts=2:sw=2:tw=80:et: