Merge 127520 - REGRESSION(r120832): RenderLayer::clampScrollOffset doesn't properly clamp
Reviewed by Simon Fraser.
* ManualTests/select-menu-list-wrongly-positioned.html: Added.
r120832 consolidated the clamping logic into RenderLayer::clampScrollOffset. The existing code wouldn't properly ensure that
the offset were positive which got exposed to other code paths, leading to the regression.
Tested by ManualTests/select-menu-list-wrongly-positioned.html as I didn't find a way to create a reliable layout test.
Fixed the clamping logic to ensure that the scroll offset's dimensions are positive.