Add a MailNotifier that notifies chrome-security-bugs--@google.com for LKGR builds.

This is a re-implementation of https://codereview.chromium.org/1241393002/.

R=inferno@chromium.org,mbarbella@chromium.org,ochang@chromium.org

Review URL: https://codereview.chromium.org/1271613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/build@296189 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/scripts/slave/gatekeeper.json b/scripts/slave/gatekeeper.json
index 45b36cc..e5c61e0 100644
--- a/scripts/slave/gatekeeper.json
+++ b/scripts/slave/gatekeeper.json
@@ -209,6 +209,18 @@
             ]
           }
         }
+      },
+      {
+        "tree_notify": [
+          "chrome-security-sheriff@grotations.appspotmail.com"
+        ],
+
+        "subject_template": "LKGR build failure on %(builder_name)s",
+
+        "forgive_all": true,
+        "builders": {
+          "*": {}
+        }
       }
     ],
     "https://build.chromium.org/p/chromium.mac": [