Break config_default into master_site_configs.

masters/master.chromium.endure/master.cfg

Index: masters/master.chromium.endure/master.cfg
diff --git a/masters/master.chromium.endure/master.cfg b/masters/master.chromium.endure/master.cfg
index f4872160a3aee32f49c7ddd912cd9a87ca076b96..510bf1ac8c79ba7bd21c1b1d45e87f53c8b139ed 100644
--- a/masters/master.chromium.endure/master.cfg
+++ b/masters/master.chromium.endure/master.cfg
@@ -13,6 +13,7 @@ from master import slaves_list
 from master.factory import chromium_factory
 
 import config
+import master_site_config
 
 _CUSTOM_DEPS_LLVM_ALLOCATED_TYPE = (
     'src/third_party/llvm-allocated-type',
@@ -34,7 +35,7 @@ _DBG_GCLIENT_ENV = {
     'GYP_GENERATORS': 'ninja',
 }
 
-ActiveMaster = config.Master.ChromiumEndure
+ActiveMaster = master_site_config.ChromiumEndure
 
 # This is the dictionary that the buildmaster pays attention to. We also use
 # a shorter alias to save typing.