Add internal copy of wpt/tools/third_party to checkperms.py exception list

As part of mandatory code review, we are moving from the copy of tools
in third_party/blink/web_tests/external/wpt/tools to the manually rolled
copy in third_party/blink/tools/blinkpy/third_party/wpt/wpt. WPT itself
has some third-party libraries that violate checkperms that we cannot
easily fix, so make those an exception.

Once the migration is completed, we will remove the previous
external/wpt/tools entry here as well.

Bug: 1165950
Change-Id: I7145b8bf4e82c8fd99ad5f42330b68e2f29aac45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2626420
Auto-Submit: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Luke Z <lpz@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843823}

tools/checkperms/checkperms.py

@@ -179,6 +179,7 @@ IGNORED_PATHS = (
       '__init__.py',
   'out/',
   'third_party/blink/web_tests/external/wpt/tools/third_party/',
+  'third_party/blink/tools/blinkpy/third_party/wpt/wpt/tools/third_party/',
   # TODO(maruel): Fix these.
   'third_party/devscripts/licensecheck.pl.vanilla',
   'third_party/libxml/linux/xml2-config',