[LayoutNG] Add layout_ng try bots for core/editing

This patch adds LayoutNG bots for changes in
core/editing directory because of deep dependency.

Bug: 707656
Change-Id: Iafcf381f9fab5c8472917c3d7ca22d8c378ba2f7
Reviewed-on: https://chromium-review.googlesource.com/1116402Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570690}

third_party/blink/PRESUBMIT.py

@@ -210,6 +210,7 @@ def _ArePaintOrCompositingDirectoriesModified(change):  # pylint: disable=C0103
 def _AreLayoutNGDirectoriesModified(change):  # pylint: disable=C0103
     """Checks whether CL has changes to a layout ng directory."""
     layout_ng_paths = [
+        os.path.join('third_party', 'blink', 'renderer', 'core', 'editing'),
         os.path.join('third_party', 'blink', 'renderer', 'core', 'layout',
                      'ng'),
         os.path.join('third_party', 'blink', 'renderer', 'core', 'paint',