Replace various ScrollableArea scroll methods with setScrollPosition

Source/platform/mac/ScrollAnimatorMac.mm

Index: Source/platform/mac/ScrollAnimatorMac.mm
diff --git a/Source/platform/mac/ScrollAnimatorMac.mm b/Source/platform/mac/ScrollAnimatorMac.mm
index 6ab30748bb030c8766b1660684868531208ea12e..3ced5e97d72f9c4134b58ead8403f3947a0ea6ed 100644
--- a/Source/platform/mac/ScrollAnimatorMac.mm
+++ b/Source/platform/mac/ScrollAnimatorMac.mm
@@ -733,10 +733,10 @@ ScrollResultOneDimensional ScrollAnimatorMac::userScroll(ScrollbarOrientation or
     return ScrollResultOneDimensional(true, delta - usedDelta);
 }
 
-void ScrollAnimatorMac::scrollToOffsetWithoutAnimation(const FloatPoint& offset)
+void ScrollAnimatorMac::scrollToOffsetWithoutAnimation(const FloatPoint& offset, ScrollType scrollType)
 {
     [m_scrollAnimationHelper.get() _stopRun];
-    immediateScrollTo(offset);
+    immediateScrollTo(offset, scrollType);
 }
 
 FloatPoint ScrollAnimatorMac::adjustScrollPositionIfNecessary(const FloatPoint& position) const
@@ -753,7 +753,7 @@ FloatPoint ScrollAnimatorMac::adjustScrollPositionIfNecessary(const FloatPoint&
     return FloatPoint(newX, newY);
 }
 
-void ScrollAnimatorMac::immediateScrollTo(const FloatPoint& newPosition)
+void ScrollAnimatorMac::immediateScrollTo(const FloatPoint& newPosition, ScrollType scrollType)
 {
     FloatPoint adjustedPosition = adjustScrollPositionIfNecessary(newPosition);
 
@@ -766,13 +766,14 @@ void ScrollAnimatorMac::immediateScrollTo(const FloatPoint& newPosition)
     m_currentPosX = adjustedPosition.x();
     m_currentPosY = adjustedPosition.y();
     notifyContentAreaScrolled(delta);
-    notifyPositionChanged();
+    notifyPositionChanged(scrollType);
 }
 
 void ScrollAnimatorMac::immediateScrollToPointForScrollAnimation(const FloatPoint& newPosition)
 {
+    // TODO(bokan): I'm no ObjC expert but this method's only caller seems to be unused.

[skobes, 2015/06/04 23:35:47]

The caller is passed into NSScrollAnimationHelper, so maybe there is some Cocoa
stuff calling it?  But I am not an Objective C expert either. :)

[bokan, 2015/06/05 15:15:23]

Doesn't look like it, it's one of the CLs I split out (just forgot this TODO).
It compiled fine on my Mac and passed the CQ dry run. This'll go away when I
land https://codereview.chromium.org/1165883002/ and rebase. 

     ASSERT(m_scrollAnimationHelper);
-    immediateScrollTo(newPosition);
+    immediateScrollTo(newPosition, ProgrammaticScroll);
 }
 
 void ScrollAnimatorMac::contentAreaWillPaint() const