Break config_default into master_site_configs.

masters/master.tryserver.nacl/master.cfg

Index: masters/master.tryserver.nacl/master.cfg
diff --git a/masters/master.tryserver.nacl/master.cfg b/masters/master.tryserver.nacl/master.cfg
index f4523b84aeb09b76942b38db89550e0e7732dfdf..cc14d355b11e6611448d7c5e2724bff7115307f3 100644
--- a/masters/master.tryserver.nacl/master.cfg
+++ b/masters/master.tryserver.nacl/master.cfg
@@ -21,8 +21,9 @@ from master.try_job_svn import TryJobSubversion
 from buildbot.scheduler import Triggerable
 
 import config
+import master_site_config
 
-ActiveMaster = config.Master.NativeClientTryServer
+ActiveMaster = master_site_config.NativeClientTryServer
 
 MAIL_NOTIFIER = True
 UPDATE_CODEREVIEW = ActiveMaster.is_production_host
@@ -620,9 +621,9 @@ c['slaves'] = master_utils.AutoSetupSlaves(c['builders'],
 c['schedulers'] = []
 
 code_review_sites = {
-  'nacl': config.Master.NativeClientTryServer.code_review_site,
-  'nacl-toolchain': config.Master.NativeClientTryServer.code_review_site,
-  'gyp': config.Master.NativeClientTryServer.code_review_site,
+  'nacl': ActiveMaster.code_review_site,
+  'nacl-toolchain': ActiveMaster.code_review_site,
+  'gyp': ActiveMaster.code_review_site,
 }
 c['schedulers'].append(TryJobHTTP(
     name='try_job_http',