Ignore recent local commits when computing the LASTCHANGE position.

For unclear reasons, the build/util/LASTCHANGE file frequently contained
the hash of a local-only commit from a working branch, and the result
was a 404 error when trying to inspect a page in devtools.

To avoid this, add a --filter regex that is passed to "git log --grep",
defaulting to '^Change-Id:'. This header is present for the main
source tree and third_party/skia/ official commits.

BUG=760304

Change-Id: I9464ba37a1197872a7ffd31b8c2f1a2a85856276
Reviewed-on: https://chromium-review.googlesource.com/949312Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Commit-Queue: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541137}

build/util/lastchange.py

@@ -46,7 +46,7 @@ def RunGitCommand(directory, command):
     return None
 
 
-def FetchGitRevision(directory):
+def FetchGitRevision(directory, filter):
   """
   Fetch the Git hash (and Cr-Commit-Position if any) for a given directory.
 
@@ -57,6 +57,8 @@ def FetchGitRevision(directory):
   """
   hsh = ''
   git_args = ['log', '-1', '--format=%H']
+  if filter is not None:
+    git_args.append('--grep=' + filter)
   proc = RunGitCommand(directory, git_args)
   if proc:
     output = proc.communicate()[0].strip()
@@ -76,12 +78,12 @@ def FetchGitRevision(directory):
   return VersionInfo(hsh, '%s-%s' % (hsh, pos))
 
 
-def FetchVersionInfo(directory=None):
+def FetchVersionInfo(directory=None, filter=None):
   """
   Returns the last change (as a VersionInfo object)
   from some appropriate revision control system.
   """
-  version_info = FetchGitRevision(directory)
+  version_info = FetchGitRevision(directory, filter)
   if not version_info:
     version_info = VersionInfo('0', '0')
   return version_info
@@ -165,10 +167,16 @@ def main(argv=None):
                     "file-output-related options.")
   parser.add_option("-s", "--source-dir", metavar="DIR",
                     help="Use repository in the given directory.")
+  parser.add_option("", "--filter", metavar="REGEX",
+                    help="Only use log entries where the commit message " +
+                    "matches the supplied filter regex. Defaults to " +
+                    "'^Change-Id:' to suppress local commits.",
+                    default='^Change-Id:')
   opts, args = parser.parse_args(argv[1:])
 
   out_file = opts.output
   header = opts.header
+  filter=opts.filter
 
   while len(args) and out_file is None:
     if out_file is None:
@@ -183,7 +191,7 @@ def main(argv=None):
   else:
     src_dir = os.path.dirname(os.path.abspath(__file__))
 
-  version_info = FetchVersionInfo(directory=src_dir)
+  version_info = FetchVersionInfo(directory=src_dir, filter=filter)
   revision_string = version_info.revision
   if opts.revision_id_only:
     revision_string = version_info.revision_id