Merge 123637 - https://bugs.webkit.org/show_bug.cgi?id=89114

Merge 123637 - https://bugs.webkit.org/show_bug.cgi?id=89114
REGRESSION (r112919): Setting scrollTop after setting display from none to block 
fails
-and corresponding-
<rdar://problem/11656050>

Reviewed by Simon Fraser.

Source/WebCore: 

ScrollAnimatorMac::immediateScrollTo() and ScrollAnimatorMac::immediateScrollBy() 
both have an optimization in place so that they do not call 
notifyPositionChanged() if the new scroll offset matches the ScrollAnimator's 
cached m_currentPosX and m_currentPosY. So revision 112919 caused troubled with 
this optimization because it allowed RenderLayers to restore a scrollOffset from 
the Element if there is one cached there. This caused the RenderLayer to have a 
scrollOffset that is improperly out-of-synch with the ScrollAnimator's 
currentPosition (which will just be 0,0 since it is being re-created like the 
RenderLayer). This fix makes sure they are in synch by calling 
setCurrentPosition() on the ScrollAnimator when the cached position is non-zero.
* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::RenderLayer):

LayoutTests: 

* fast/overflow/setting-scrollTop-after-hide-show-expected.txt: Added.
* fast/overflow/setting-scrollTop-after-hide-show.html: Added.



TBR=karen@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=125733