[NaCl SDK] Use chromium trybots when making changes to native_client_sdk.

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 9a7a68034e6cd7a7e9e1bf77968caac6183f8aea..55e56d80a78d6af13ab788e31f4c0a20bac4ce41 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -607,6 +607,8 @@ def GetPreferredTrySlaves(project, change):
     return ['win_rel']
   if all(re.search('(^|[/_])android[/_.]', f) for f in files):
     return ['android_dbg']
+  if all(re.search('^native_client_sdk', f) for f in files):
+    return ['linux_nacl_sdk', 'win_nacl_sdk', 'mac_nacl_sdk']
 
   trybots = ['win_rel', 'linux_rel', 'mac_rel', 'linux_clang:compile',
              'linux_chromeos', 'android_dbg', 'linux_asan', 'mac_asan']