Temporarily make lastchange use only the git hash.

This will fix the currently failing browser_tests
CloudPolicyTests, which fail because the lastchange
string is too long.

TBR=scottmg@chromium.org, tandrii@chromium.org
NOTRY=True
NOTREECHECKS=True
TEST=passed browser_tests on linux_chromium_rel trybot
BUG=406783

Review URL: https://codereview.chromium.org/499063002

Cr-Commit-Position: refs/heads/master@{#291571}

build/util/lastchange.py

@@ -99,6 +99,8 @@ def FetchGitRevision(directory):
   Returns:
     A VersionInfo object or None on error.
   """
+  # TODO(agable): Re-add the commit position after the lastchange value can
+  # accept strings longer than 64 characters. See crbug.com/406783.
   hsh = ''
   proc = RunGitCommand(directory, ['rev-parse', 'HEAD'])
   if proc:
@@ -107,17 +109,7 @@ def FetchGitRevision(directory):
       hsh = output
   if not hsh:
     return None
-  pos = ''
-  proc = RunGitCommand(directory, ['show', '-s', '--format=%B', 'HEAD'])
-  if proc:
-    output = proc.communicate()[0]
-    if proc.returncode == 0 and output:
-      for line in reversed(output.splitlines()):
-        if line.startswith('Cr-Commit-Position:'):
-          pos = line.rsplit()[-1].strip()
-  if not pos:
-    return VersionInfo('git', hsh)
-  return VersionInfo('git', '%s-%s' % (hsh, pos))
+  return VersionInfo('git', hsh)
 
 
 def FetchGitSVNURLAndRevision(directory, svn_url_regex):