depot_tools: Add git svn find-rev for safesync_url parsing (commonly LKGR link).

gclient.py

Index: gclient.py
===================================================================
--- gclient.py	(revision 108803)
+++ gclient.py	(working copy)
@@ -923,8 +923,13 @@
           handle = urllib.urlopen(s.safesync_url)
           rev = handle.read().strip()
           handle.close()
-          if len(rev):
-            self._options.revisions.append('%s@%s' % (s.name, rev))
+          scm = gclient_scm.CreateSCM(s.url, s.root.root_dir, s.name)
+          safe_rev = scm.FindSafesyncRev(
+              cwd=scm.checkout_path, rev=rev, options=self._options)
+          if safe_rev:
+            if self._options.verbose:
+              print('Using safesync_url revision: %s.\n' % safe_rev) 
+            self._options.revisions.append('%s@%s' % (s.name, safe_rev))
     if not self._options.revisions:
       return revision_overrides
     solutions_names = [s.name for s in self.dependencies]