Update masters after the tryserver split.

chrome/browser/sync/PRESUBMIT.py

Index: chrome/browser/sync/PRESUBMIT.py
diff --git a/chrome/browser/sync/PRESUBMIT.py b/chrome/browser/sync/PRESUBMIT.py
index a5b9f434636fe2818703c802865332769a8b1a37..137ad33046ec7503e07357f1f8e05a9ae9544e0c 100644
--- a/chrome/browser/sync/PRESUBMIT.py
+++ b/chrome/browser/sync/PRESUBMIT.py
@@ -10,9 +10,13 @@ for more details on the presubmit API built into gcl.
 
 def GetPreferredTryMasters(project, change):
   return {
-    'tryserver.chromium': {
-      'linux_chromium_rel': set(['defaulttests']),
+    'tryserver.chromium.linux': {
+      'linux_chromium_rel_swarming': set(['defaulttests']),
+    },
+    'tryserver.chromium.mac': {
       'mac_chromium_rel': set(['defaulttests']),
+    },
+    'tryserver.chromium.win': {
       'win_chromium_rel': set(['defaulttests']),
     }
   }