Move ScrollingThread to its own file

Move ScrollingThread to its own file
https://bugs.webkit.org/show_bug.cgi?id=77652

Reviewed by Sam Weinig.

This just shuffles some classes around and makes ScrollingCoordinator call into ScrollingThread.
Hopefully we'll be able to make ScrollingThread use the new WebCore::RunLoop class eventually.

* WebCore.xcodeproj/project.pbxproj:
* page/scrolling/ScrollingCoordinator.cpp:
(WebCore::ScrollingCoordinator::handleWheelEvent):
* page/scrolling/ScrollingCoordinator.h:
(ScrollingCoordinator):
* page/scrolling/ScrollingThread.cpp: Added.
(WebCore):
(WebCore::ScrollingThread::ScrollingThread):
(WebCore::ScrollingThread::isCurrentThread):
(WebCore::ScrollingThread::dispatch):
(WebCore::ScrollingThread::shared):
(WebCore::ScrollingThread::createThreadIfNeeded):
(WebCore::ScrollingThread::threadCallback):
(WebCore::ScrollingThread::threadBody):
(WebCore::ScrollingThread::dispatchFunctionsFromScrollingThread):
* page/scrolling/ScrollingThread.h: Added.
(WebCore):
(ScrollingThread):
* page/scrolling/mac/ScrollingCoordinatorMac.mm:
(WebCore::ScrollingCoordinator::scrollByOnScrollingThread):
(WebCore::ScrollingCoordinator::updateMainFrameScrollLayerPositionOnScrollingThread):
* page/scrolling/mac/ScrollingThreadMac.mm: Added.
(WebCore):
(WebCore::ScrollingThread::initializeRunLoop):
(WebCore::ScrollingThread::wakeUpRunLoop):
(WebCore::ScrollingThread::threadRunLoopSourceCallback):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106565 268f45cc-cd09-0410-ab3c-d52691b4dbfc