[depot_tools] Use git fetch to optimize the properly configured that use git-svn

gclient_scm.py

Index: gclient_scm.py
diff --git a/gclient_scm.py b/gclient_scm.py
index 211aa473792fa4d218c6ab8cddc09b96bc837a99..00013465859c7960e34cc4126bef3cf7a13c7d34 100644
--- a/gclient_scm.py
+++ b/gclient_scm.py
@@ -500,6 +500,14 @@ class GitWrapper(SCMWrapper):
           scm.GIT.IsGitSvn(cwd=self.checkout_path)):
         local_head = scm.GIT.GetGitSvnHeadRev(cwd=self.checkout_path)
         if not local_head or local_head < int(rev):
+          try:
+            logging.debug('Looking for git-svn configuration optimizations.')
+            if scm.GIT.Capture(['config', '--get', 'svn-remote.svn.fetch'],
+                             cwd=self.checkout_path):
+              scm.GIT.Capture(['fetch'], cwd=self.checkout_path)
+          except subprocess2.CalledProcessError:
+            logging.debug('git config --get svn-remote.svn.fetch failed, '
+                          'ignoring possible optimization.')
           if options.verbose:
             print('Running git svn fetch. This might take a while.\n')
           scm.GIT.Capture(['svn', 'fetch'], cwd=self.checkout_path)