PRESUBMIT: use "master." prefix in CQ_INCLUDE_TRYBOTS.

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index d60a19cccd0d687f102d1be589593b36cae4421e..8a47288525d8ab3c8fe4dcfc4585e9f4351f3594 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -2182,19 +2182,19 @@ def GetTryServerMasterForBot(bot):
   """
   # Potentially ambiguous bot names are listed explicitly.
   master_map = {
-      'chromium_presubmit': 'tryserver.chromium.linux',
-      'tools_build_presubmit': 'tryserver.chromium.linux',
+      'chromium_presubmit': 'master.tryserver.chromium.linux',
+      'tools_build_presubmit': 'master.tryserver.chromium.linux',
   }
   master = master_map.get(bot)
   if not master:
     if 'android' in bot:
-      master = 'tryserver.chromium.android'
+      master = 'master.tryserver.chromium.android'
     elif 'linux' in bot or 'presubmit' in bot:
-      master = 'tryserver.chromium.linux'
+      master = 'master.tryserver.chromium.linux'
     elif 'win' in bot:
-      master = 'tryserver.chromium.win'
+      master = 'master.tryserver.chromium.win'
     elif 'mac' in bot or 'ios' in bot:
-      master = 'tryserver.chromium.mac'
+      master = 'master.tryserver.chromium.mac'
   return master