Make correction to grep pattern to grab git hash for given commit position.

tools/auto_bisect/source_control.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.
 
 """This module contains the SourceControl class and related functions."""
 
 import os
 
 from . import bisect_utils
 
@@ skipping 136 matching lines @@
       svn_revision = int(revision_to_check)
       git_revision = None
 
       if search > 0:
         search_range = xrange(svn_revision, svn_revision + search, 1)
       else:
         search_range = xrange(svn_revision, svn_revision + search, -1)
 
       for i in search_range:
         svn_pattern = 'git-svn-id: %s@%d' % (depot_svn, i)
-        commit_position_pattern = 'Cr-Commit-Position: .*@{#%d}' % i
+        commit_position_pattern = '^Cr-Commit-Position: .*@{#%d}' % i
         cmd = ['log', '--format=%H', '-1', '--grep', svn_pattern,
                '--grep', commit_position_pattern, 'origin/master']
 
         (log_output, return_code) = bisect_utils.RunGit(cmd, cwd=cwd)
 
         assert not return_code, 'An error occurred while running'\
                                 ' "git %s"' % ' '.join(cmd)
 
         if not return_code:
           log_output = log_output.strip()
@@ skipping 117 matching lines @@
         revision_end: End of revision range.
 
     Returns:
         Returns a list of commits that touched this file.
     """
     cmd = ['log', '--format=%H', '%s~1..%s' % (revision_start, revision_end),
            '--', filename]
     output = bisect_utils.CheckRunGit(cmd)
 
     return [o for o in output.split('\n') if o]