Support for |change| argument to |GetPreferredTrySlaves()|, try 2.

gcl.py

Index: gcl.py
===================================================================
--- gcl.py	(revision 102922)
+++ gcl.py	(working copy)
@@ -961,11 +961,21 @@
     if change_info.patchset:
       trychange_args.extend(["--patchset", str(change_info.patchset)])
     file_list = change_info.GetFileNames()
+    change = presubmit_support.SvnChange(change_info.name,
+                                         change_info.description,
+                                         change_info.GetLocalRoot(),
+                                         change_info.GetFiles(),
+                                         change_info.issue,
+                                         change_info.patchset,
+                                         None)
   else:
     file_list = []
+    change = None
+
   trychange_args.extend(args)
   return trychange.TryChange(
       trychange_args,
+      change=change,
       file_list=file_list,
       swallow_exception=swallow_exception,
       prog='gcl try',