Add job prefix to error messages.

BUG=235289
R=maruel@chromium.org

Review URL: https://codereview.chromium.org/15792004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@202236 0039d316-1c4b-4281-b951-d872f2087c98

gclient_utils.py

@@ -22,8 +22,11 @@ import subprocess2
 
 class Error(Exception):
   """gclient exception class."""
-  pass
-
+  def __init__(self, msg, *args, **kwargs):
+    index = getattr(threading.currentThread(), 'index', 0)
+    if index:
+      msg = '\n'.join('%d> %s' % (index, l) for l in msg.splitlines())
+    super(Error, self).__init__(msg, *args, **kwargs)
 
 def SplitUrlRevision(url):
   """Splits url and returns a two-tuple: url, rev"""