Autoroll: Update checkout before reading chromium_revision.

tools/autoroller/roll_chromium_revision.py

 #!/usr/bin/env python
 # Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 """Script to roll chromium_revision in the WebRTC DEPS file."""
@@ skipping 279 matching lines @@
     deps_file.write(deps_content)
 
 def _IsTreeClean():
   stdout, _ = _RunCommand(['git', 'status', '--porcelain'])
   if len(stdout) == 0:
     return True
 
   logging.error('Dirty/unversioned files:\n%s', stdout)
   return False
 
-def _CreateRollBranch(dry_run):
+
+def _EnsureUpdatedMasterBranch(dry_run):
   current_branch = _RunCommand(
       ['git', 'rev-parse', '--abbrev-ref', 'HEAD'])[0].splitlines()[0]
   if current_branch != 'master':
     logging.error('Please checkout the master branch and re-run this script.')
     if not dry_run:
       sys.exit(-1)
 
   logging.info('Updating master branch...')
   if not dry_run:
     _RunCommand(['git', 'pull'])
+
+
+def _CreateRollBranch(dry_run):
   logging.info('Creating roll branch: %s', ROLL_BRANCH_NAME)
   if not dry_run:
     _RunCommand(['git', 'checkout', '-b', ROLL_BRANCH_NAME])
 
 
 def _RemovePreviousRollBranch(dry_run):
   active_branch, branches = _GetBranches()
   if active_branch == ROLL_BRANCH_NAME:
     active_branch = 'master'
   if ROLL_BRANCH_NAME in branches:
@@ skipping 44 matching lines @@
   else:
     logging.basicConfig(level=logging.INFO)
 
   if not _IsTreeClean():
     logging.error('Please clean your local checkout first.')
     return 1
 
   if opts.clean:
     _RemovePreviousRollBranch(opts.dry_run)
 
+  _EnsureUpdatedMasterBranch(opts.dry_run)
+
   if not opts.revision:
     lkgr_contents = ReadUrlContent(CHROMIUM_LKGR_URL)
     logging.info('No revision specified. Using LKGR: %s', lkgr_contents[0])
     opts.revision = lkgr_contents[0]
 
   deps_filename = os.path.join(CHECKOUT_ROOT_DIR, 'DEPS')
   local_deps = ParseLocalDepsFile(deps_filename)
   current_cr_rev = local_deps['vars']['chromium_revision']
 
   current_cr_deps = ParseRemoteCrDepsFile(current_cr_rev)
@@ skipping 13 matching lines @@
   _CreateRollBranch(opts.dry_run)
   UpdateDeps(deps_filename, current_cr_rev, opts.revision)
   _LocalCommit(commit_msg, opts.dry_run)
   _UploadCL(opts.dry_run)
   _LaunchTrybots(opts.dry_run, opts.skip_try)
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())