Split up ESLint rules configurations in sub-folders

I have locally verified that adding an `it.only` in our test
suite correctly fails the ESLint process.

R=jacktfranklin@chromium.org

Fixed: 1158382
Change-Id: Id9b267e2b814f1d5ea85ff46d325d2a91030b2a2
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2587745
Commit-Queue: Tim van der Lippe <tvanderlippe@chromium.org>
Reviewed-by: Jack Franklin <jacktfranklin@chromium.org>
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index cd7e403..81f3146 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -209,6 +209,7 @@
         input_api.os_path.join(input_api.PresubmitLocalPath(),
                                '.eslintignore'),
         input_api.os_path.join(front_end_directory, '.eslintrc.js'),
+        input_api.os_path.join(test_directory, '.eslintrc.js'),
         input_api.os_path.join(scripts_directory, 'test',
                                'run_lint_check_js.py'),
         input_api.os_path.join(scripts_directory, 'test',