Add CQ_INCLUDE_TRYBOTS for GN header checkers

BUG=661774

Review-Url: https://codereview.chromium.org/2936433002
Cr-Commit-Position: refs/heads/master@{#478800}

build/PRESUBMIT.py

+# Copyright (c) 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Presubmit script for //build.
+
+See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
+for more details about the presubmit API built into depot_tools.
+"""
+
+def PostUploadHook(cl, change, output_api):
+  """git cl upload will call this hook after the issue is created/modified.
+
+  This hook modifies the CL description in order to run extra tests.
+  """
+
+  def affects_gn_checker(f):
+    return 'check_gn_headers' in f.LocalPath()
+  if not change.AffectedFiles(file_filter=affects_gn_checker):
+    return []
+  return output_api.EnsureCQIncludeTrybotsAreAdded(
+    cl,
+    [
+      'master.tryserver.chromium.linux:linux_chromium_dbg_ng',
+    ],
+    'Automatically added tests to run on CQ.')