fix incorrect use of string identity tests

Strings should not use "is" to test equivalence as that is an object
identity test, not a string compare test.  It happens to work most of
the time, but better to be correct.

BUG=None
TEST=precq passes

Change-Id: If983681e87cf261228a4454d9c4d0dcf7b49a330
Reviewed-on: https://chromium-review.googlesource.com/565840
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Allen Li <ayatane@chromium.org>
diff --git a/scripts/sync_chrome.py b/scripts/sync_chrome.py
index c0cf7fb..eec738f 100644
--- a/scripts/sync_chrome.py
+++ b/scripts/sync_chrome.py
@@ -52,7 +52,7 @@
   parser = GetParser()
   options = parser.parse_args(argv)
 
-  if options.gclient is '':
+  if options.gclient == '':
     parser.error('--gclient can not be an empty string!')
   gclient_path = options.gclient or osutils.Which('gclient')
   if not gclient_path: