Add GN bots into commit queue

infra/config/cq.cfg

 # See http://luci-config.appspot.com/schemas/projects/refs:cq.cfg for the
 # documentation of this file format.
 
 version: 1
 cq_name: "pdfium"
 git_repo_url: "https://pdfium.googlesource.com/pdfium.git"
 cq_status_url: "https://chromium-cq-status.appspot.com"
 
 rietveld {
   url: "https://codereview.chromium.org"
@@ skipping 31 matching lines @@
       }
       builders {
         name: "win"
       }
       builders {
         name: "win_xfa"
       }
       builders {
         name: "win_no_v8"
       }
+      builders {
+        name: "linux_xfa_rel_gn"

[Lei Zhang, 2016/05/12 22:12:02]

Do we want to keep them grouped as linux/mac/win?

[Wei Li, 2016/05/12 22:33:33]

For now, let's group into gn so we can clearly see whether an error is tied to
the build system. After the transition, we will regroup them.

+      }
+      builders {
+        name: "mac_xfa_rel_gn"
+      }
+      builders {
+        name: "win_xfa_64_rel_gn"
+      }
     }
   }
 }