Turn on threaded scrolling by default in the tests

Turn on threaded scrolling by default in the tests
https://bugs.webkit.org/show_bug.cgi?id=149377

Reviewed by Simon Fraser.

* WebKitTestRunner/mac/TestControllerMac.mm:
(WTR::TestController::updatePlatformSpecificTestOptionsForTest):
(WTR::shouldUseThreadedScrolling): Deleted.
Turn on threaded scrolling by default.

* compositing/geometry/fixed-position-flipped-writing-mode.html:
* compositing/layer-creation/no-compositing-for-sticky.html:
* compositing/overflow/automatically-opt-into-composited-scrolling.html:
* compositing/overflow/clipping-ancestor-with-accelerated-scrolling-ancestor.html:
* compositing/overflow/composited-scrolling-creates-a-stacking-container.html:
* compositing/overflow/composited-scrolling-paint-phases.html:
* compositing/overflow/do-not-paint-outline-into-composited-scrolling-contents.html:
* compositing/overflow/dynamic-composited-scrolling-status.html:
* compositing/overflow/iframe-inside-overflow-clipping.html:
* compositing/overflow/nested-scrolling.html:
* compositing/overflow/overflow-clip-with-accelerated-scrolling-ancestor.html:
* compositing/overflow/paint-neg-z-order-descendants-into-scrolling-contents-layer.html:
* compositing/overflow/scrolling-content-clip-to-viewport.html:
* compositing/overflow/scrolling-without-painting.html:
* compositing/overflow/textarea-scroll-touch.html:
* compositing/overflow/updating-scrolling-content.html:
* compositing/rtl/rtl-fixed-overflow-scrolled.html:
* compositing/rtl/rtl-overflow-scrolling.html:
* fast/block/positioning/rtl-fixed-positioning.html:
* fast/block/positioning/vertical-rl/fixed-positioning.html:
* fast/dom/horizontal-scrollbar-in-rtl.html:
* fast/dom/horizontal-scrollbar-when-dir-change.html:
* fast/dom/scroll-reveal-left-overflow.html:
* fast/dom/scroll-reveal-top-overflow.html:
* fast/dom/vertical-scrollbar-when-dir-change.html:
* fast/multicol/pagination/RightToLeft-rl-hittest.html:
* scrollingcoordinator/non-fast-scrollable-region-scaled-iframe.html:
* scrollingcoordinator/non-fast-scrollable-region-transformed-iframe.html:
* swipe/main-frame-pinning-requirement.html:
Turn off threaded scrolling in the cases where it sensibly affects the test result.
These cases are:
        - tests that use scrollTo or similar, and then depend on the
          scrolling happening synchronously

        - tests that use setAcceleratedCompositingForOverflowScrollEnabled,
          which asserts if combined with threaded scrolling

* fast/text/combining-character-sequence-vertical.html:
* fast/text/descent-clip-in-scaled-page.html:
* fast/text/descent-clip-in-scaled-page-expected.html:
* fast/text/vertical-quotation-marks.html:
Turn off threaded scrolling in three tests where it shouldn't affect the test result,
but for some reason does.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@190060 268f45cc-cd09-0410-ab3c-d52691b4dbfc