[ChromeDriver] Fix version string in release branch

The previous change (r581945) to update version string used by
ChromeDriver in release branches didn't work, because the top-most
commit doesn't have the necessary branch info. This CL adds the same
commit filter used to generate the version string shown by Chrome.

Bug: chromedriver:2080
Change-Id: I4d7b57a139968d3e5e0f1ebad26d6ed648ab5d72
Reviewed-on: https://chromium-review.googlesource.com/1171843Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582404}

chrome/test/chromedriver/embed_version_in_cpp.py

@@ -84,11 +84,12 @@ def main():
   chromedriver_version = open(
       options.chromedriver_version_file, 'r').read().strip()
 
-  # Get a VersionInfo object corresponding to the Git commit we are at.
+  # Get a VersionInfo object corresponding to the Git commit we are at,
+  # using the same filter used by main function of build/util/lastchange.py.
   # On success, version_info.revision_id is a 40-digit Git hash,
   # and version_info.revision is a longer string with more information.
   # On failure, version_info is None.
-  version_info = lastchange.FetchGitRevision(None, None)
+  version_info = lastchange.FetchGitRevision(None, '^Change-Id:')
 
   if version_info:
     version = get_release_version(options.chrome_version_file, version_info)