[Cocoa] Rename ScrollbarPainter variables to ScrollerImp

[Cocoa] Rename ScrollbarPainter variables to ScrollerImp
https://bugs.webkit.org/show_bug.cgi?id=155976

Reviewed by Simon Fraser.

This patch continues where r198078 left off. That patch renamed all the types,
however, there are some variables which were left as "scrollbarPainter". This
patch completes the transition to ScrollerImp.

No new tests because there is no behavior change.

* platform/mac/ScrollAnimatorMac.h:
* platform/mac/ScrollAnimatorMac.mm:
(scrollerImpForScrollbar):
(-[WebScrollerImpPairDelegate scrollerImpPair:convertContentPoint:toScrollerImp:]):
(-[WebScrollbarPartAnimation startAnimation]):
(-[WebScrollbarPartAnimation setCurrentProgress:]):
(-[WebScrollerImpDelegate mouseLocationInScrollerForScrollerImp:]):
(-[WebScrollerImpDelegate scrollerImp:animateKnobAlphaTo:duration:]):
(-[WebScrollerImpDelegate scrollerImp:animateTrackAlphaTo:duration:]):
(-[WebScrollerImpDelegate scrollerImp:animateUIStateTransitionWithDuration:]):
(-[WebScrollerImpDelegate scrollerImp:animateExpansionTransitionWithDuration:]):
(WebCore::ScrollAnimatorMac::ScrollAnimatorMac):
(WebCore::ScrollAnimatorMac::~ScrollAnimatorMac):
(WebCore::ScrollAnimatorMac::contentAreaWillPaint):
(WebCore::ScrollAnimatorMac::mouseEnteredContentArea):
(WebCore::ScrollAnimatorMac::mouseExitedContentArea):
(WebCore::ScrollAnimatorMac::mouseMovedInContentArea):
(WebCore::ScrollAnimatorMac::mouseEnteredScrollbar):
(WebCore::ScrollAnimatorMac::mouseExitedScrollbar):
(WebCore::ScrollAnimatorMac::mouseIsDownInScrollbar):
(WebCore::ScrollAnimatorMac::willStartLiveResize):
(WebCore::ScrollAnimatorMac::contentsResized):
(WebCore::ScrollAnimatorMac::willEndLiveResize):
(WebCore::ScrollAnimatorMac::contentAreaDidShow):
(WebCore::ScrollAnimatorMac::contentAreaDidHide):
(WebCore::ScrollAnimatorMac::didBeginScrollGesture):
(WebCore::ScrollAnimatorMac::didEndScrollGesture):
(WebCore::ScrollAnimatorMac::mayBeginScrollGesture):
(WebCore::ScrollAnimatorMac::lockOverlayScrollbarStateToHidden):
(WebCore::ScrollAnimatorMac::scrollbarsCanBeActive):
(WebCore::ScrollAnimatorMac::didAddVerticalScrollbar):
(WebCore::ScrollAnimatorMac::willRemoveVerticalScrollbar):
(WebCore::ScrollAnimatorMac::didAddHorizontalScrollbar):
(WebCore::ScrollAnimatorMac::willRemoveHorizontalScrollbar):
(WebCore::ScrollAnimatorMac::invalidateScrollbarPartLayers):
(WebCore::ScrollAnimatorMac::verticalScrollbarLayerDidChange):
(WebCore::ScrollAnimatorMac::horizontalScrollbarLayerDidChange):
(WebCore::ScrollAnimatorMac::shouldScrollbarParticipateInHitTesting):
(WebCore::ScrollAnimatorMac::notifyContentAreaScrolled):
(WebCore::ScrollAnimatorMac::updateScrollerStyle):
(WebCore::ScrollAnimatorMac::initialScrollbarPaintTimerFired):
(WebCore::ScrollAnimatorMac::sendContentAreaScrolled):
(scrollbarPainterForScrollbar): Deleted.
* platform/mac/ScrollbarThemeMac.mm:
(WebCore::ScrollbarThemeMac::registerScrollbar):
(WebCore::ScrollbarThemeMac::scrollbarThickness):
(WebCore::scrollerImpPaint):
(WebCore::ScrollbarThemeMac::paint):
(WebCore::scrollbarPainterPaint): Deleted.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@198787 268f45cc-cd09-0410-ab3c-d52691b4dbfc