[NaCl SDK] Fix the SDK builders to use Cr-Commit-Position.

We are relying on lastchange.FetchVersionInfo in build_sdk.py. The revision
changed from being an SVN revision to a git sha, but we want to be able to
compare the values numerically.

This change modifies build_version.py to get "Cr-Commit-Position", which for
our purposes is functionally equivalent to the SVN revision.

BUG=none
R=bradnelson@google.com, bradnelson@chromium.org

Review URL: https://codereview.chromium.org/507883003

Cr-Commit-Position: refs/heads/master@{#292179}

native_client_sdk/src/build_tools/build_version.py

@@ -6,6 +6,7 @@
 """
 
 import os
+import re
 import sys
 
 # pylint: disable=E0602
@@ -27,7 +28,7 @@ def ChromeVersion():
   Returns:
     Chrome version string or trunk + svn rev.
   '''
-  info = lastchange.FetchVersionInfo(None)
+  info = FetchVersionInfo()
   if info.url.startswith('/trunk/'):
     return 'trunk.%s' % info.revision
   else:
@@ -58,10 +59,15 @@ def ChromeMajorVersion():
 def ChromeRevision():
   '''Extract chrome revision from svn.
 
+     Now that the Chrome source-of-truth is git, this will return the
+     Cr-Commit-Position instead. fortunately, this value is equal to the SVN
+     revision if one exists.
+
   Returns:
     The Chrome revision as a string. e.g. "12345"
   '''
-  return lastchange.FetchVersionInfo(None).revision
+  return FetchVersionInfo().revision
+
 
 def NaClRevision():
   '''Extract NaCl revision from svn.
@@ -70,4 +76,48 @@ def NaClRevision():
     The NaCl revision as a string. e.g. "12345"
   '''
   nacl_dir = os.path.join(SRC_DIR, 'native_client')
-  return lastchange.FetchVersionInfo(None, nacl_dir).revision
+  return FetchVersionInfo(nacl_dir, 'native_client').revision
+
+
+def FetchVersionInfo(directory=None,
+                     directory_regex_prior_to_src_url='chrome|blink|svn'):
+  """
+  Returns the last change (in the form of a branch, revision tuple),
+  from some appropriate revision control system.
+
+  TODO(binji): This is copied from lastchange.py. Remove this function and use
+  lastchange.py directly when the dust settles. (see crbug.com/406783)
+  """
+  svn_url_regex = re.compile(
+      r'.*/(' + directory_regex_prior_to_src_url + r')(/.*)')
+
+  version_info = (lastchange.FetchSVNRevision(directory, svn_url_regex) or
+                  lastchange.FetchGitSVNRevision(directory, svn_url_regex) or
+                  FetchGitCommitPosition(directory))
+  if not version_info:
+    version_info = lastchange.VersionInfo(None, None)
+  return version_info
+
+
+def FetchGitCommitPosition(directory=None):
+  """
+  Return the "commit-position" of the Chromium git repo. This should be
+  equivalent to the SVN revision if one eixsts.
+
+  This is a copy of the (recently reverted) change in lastchange.py.
+  TODO(binji): Move this logic to lastchange.py when the dust settles.
+  (see crbug.com/406783)
+  """
+  proc = lastchange.RunGitCommand(directory,
+                                  ['show', '-s', '--format=%B', 'HEAD'])
+  pos = ''
+  if proc:
+    output = proc.communicate()[0]
+    if proc.returncode == 0 and output:
+      for line in reversed(output.splitlines()):
+        match = re.search('Cr-Commit-Position: .*@{#(\d+)}', line)
+        if match:
+          pos = match.group(1)
+  if not pos:
+    return lastchange.VersionInfo(None, None)
+  return lastchange.VersionInfo('git', pos)