Add a test ensuring that scrolling in the middle of a page can't start a swipe gesture

Add a test ensuring that scrolling in the middle of a page can't start a swipe gesture
https://bugs.webkit.org/show_bug.cgi?id=148904

Reviewed by Myles Maxfield.

* swipe/main-frame-pinning-requirement.html: Added.

* WebKitTestRunner/TestController.cpp:
(WTR::parseBooleanTestHeaderValue):
(WTR::updateViewOptionsFromTestHeader):
Check for the key "useThreadedScrolling".
Add some code to check for "true" and "false" for boolean options.

(WTR::TestController::viewOptionsForTest):
Apply the test's overrides last, even after the platform's.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@189922 268f45cc-cd09-0410-ab3c-d52691b4dbfc