git cl: cache also LABELS data on a change.

This removes 1 RPC when tbr-ing second or later patchset.

Since tests cover TBR only in first upload, there are
no test changes. Since adding test is real PITA here,
keep them as is.

R=ehmaldonado

Change-Id: I90801b06727ce2131a703d6cd6c24ffad798bc8a
Reviewed-on: https://chromium-review.googlesource.com/1242212
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
diff --git a/git_cl.py b/git_cl.py
index 5a66386..b9d8acf 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -2452,7 +2452,7 @@
     # Warm change details cache now to avoid RPCs later, reducing latency for
     # developers.
     self._GetChangeDetail(
-        ['DETAILED_ACCOUNTS', 'CURRENT_REVISION', 'CURRENT_COMMIT'])
+        ['DETAILED_ACCOUNTS', 'CURRENT_REVISION', 'CURRENT_COMMIT', 'LABELS'])
 
     status = self._GetChangeDetail()['status']
     if status in ('MERGED', 'ABANDONED'):