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

third_party/tcmalloc/PRESUBMIT.py

Index: third_party/tcmalloc/PRESUBMIT.py
diff --git a/third_party/tcmalloc/PRESUBMIT.py b/third_party/tcmalloc/PRESUBMIT.py
index 8675618f30950ba31a94cf90666d063a043808eb..f9c2c5d24fb64e3db09031d6a081f0175f9f6a49 100755
--- a/third_party/tcmalloc/PRESUBMIT.py
+++ b/third_party/tcmalloc/PRESUBMIT.py
@@ -8,5 +8,9 @@ See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details on the presubmit API built into gcl.
 """
 
-def GetPreferredTrySlaves():
-  return ['linux_valgrind']
+def GetPreferredTryMasters(project, change):
+  return {
+    'tryserver.chromium': {
+      'linux_valgrind': set(['defaulttests']),
+    }
+  }