Add linux_chromium_headless_dbg trybot builder and slaves

masters/master.tryserver.chromium.linux/slaves.cfg

Index: masters/master.tryserver.chromium.linux/slaves.cfg
diff --git a/masters/master.tryserver.chromium.linux/slaves.cfg b/masters/master.tryserver.chromium.linux/slaves.cfg
index 4c796b081896542589867fa648712298146f5040..ad4c396b0894b5d005bfb5071b226709dfd03196 100644
--- a/masters/master.tryserver.chromium.linux/slaves.cfg
+++ b/masters/master.tryserver.chromium.linux/slaves.cfg
@@ -188,6 +188,19 @@ def linux():
     }
   ])
 
+  # Slaves for linux_chromium_headless_dbg.
+  headless_slaves = [426, 497, 776, 864, 865, 872] + range(1069, 1098)
+  for slave in headless_slaves:
+    result.append({
+      'master': 'TryServerChromiumLinux',
+      'os': 'linux',
+      'version': 'trusty',
+      'bits': 64,
+      'builder': ['linux_chromium_headless_dbg'],
+      'hostname': 'slave%d-c4' % slave,
+      'pool': 'linux_chromium_headless_dbg',
+    })
+
   return result