Convert most Chromium presubmit files to use new multiple-tryserver-compatible protocol

tools/valgrind/memcheck/PRESUBMIT.py

Index: tools/valgrind/memcheck/PRESUBMIT.py
diff --git a/tools/valgrind/memcheck/PRESUBMIT.py b/tools/valgrind/memcheck/PRESUBMIT.py
index 512da0b34672c539bb30b9e07aa453ed3392f71c..0eb54d874fa5624bfd3f0740f07213a981cf91e3 100644
--- a/tools/valgrind/memcheck/PRESUBMIT.py
+++ b/tools/valgrind/memcheck/PRESUBMIT.py
@@ -77,5 +77,10 @@ def CheckChangeOnUpload(input_api, output_api):
 def CheckChangeOnCommit(input_api, output_api):
   return CheckChange(input_api, output_api)
 
-def GetPreferredTrySlaves():
-  return ['linux_valgrind', 'mac_valgrind']
+def GetPreferredTryMasters(project, change):
+  return {
+    'tryserver.chromium': {
+      'linux_valgrind': set(['defaulttests']),
+      'mac_valgrind': set(['defaulttests']),
+    }
+  }