Import W3C web platform tests infrastructure

Import W3C web platform tests infrastructure
https://bugs.webkit.org/show_bug.cgi?id=140934

Reviewed by Ryosuke Niwa.

LayoutTests/imported/w3c:

Initial import of the web-platform-tests repository.
This includes all infrastructure folders.
web-platform-tests submodules are downloaded when needed based on resources/WPTModules.

This patch also adds two tests from the domparsing folder to ensure
W3C test infrastructure works properly on WebKit bots.

* resources/WPTModules: Added
* web-platform-tests/.gitignore: Added.
* web-platform-tests/_certs: Added.
* web-platform-tests/common: Added.
* web-platform-tests/config.default.json: Added.
* web-platform-tests/fonts: Added.
* web-platform-tests/images: Added.
* web-platform-tests/resource: Added.
* web-platform-tests/serve.py: Added.
* web-platform-tests/tools: Added.
* web-platform-tests/w3c-import.log: Added
* web-platform-tests/domparsing/DOMParser-parseFromString-html-expected.txt: Added.
* web-platform-tests/domparsing/DOMParser-parseFromString-html.html: Added.
* web-platform-tests/domparsing/insert-adjacent-expected.txt: Added.
* web-platform-tests/domparsing/insert-adjacent.html: Added.
* web-platform-tests/domparsing/w3c-import.log: Added.

Tools:

Loading necessary web platform tests modules before launching server.
Ensuring that some empty __init__.py files are present and create them if necessary.

* Scripts/webkitpy/layout_tests/servers/web_platform_test_launcher.py:
* Scripts/webkitpy/layout_tests/servers/web_platform_test_server.py:

LayoutTests:

* TestExpectations: added lines to skip web-platform-tests
infrastructure folders. Added one line for a partially passing test.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@179439 268f45cc-cd09-0410-ab3c-d52691b4dbfc