Reland "Recompute overflow after transform changes"

Source/core/rendering/RenderLayerScrollableArea.cpp

Index: Source/core/rendering/RenderLayerScrollableArea.cpp
diff --git a/Source/core/rendering/RenderLayerScrollableArea.cpp b/Source/core/rendering/RenderLayerScrollableArea.cpp
index d341b15c297482c8479e09e707bee5f24d4a2da6..d31a2aed74c5a4ff911402d8b5318888397ca617 100644
--- a/Source/core/rendering/RenderLayerScrollableArea.cpp
+++ b/Source/core/rendering/RenderLayerScrollableArea.cpp
@@ -771,6 +771,26 @@ void RenderLayerScrollableArea::updateAfterCompositingChange()
     layer()->updateScrollingStateAfterCompositingChange();
 }
 
+void RenderLayerScrollableArea::updateAfterOverflowRecalc()
+{
+    computeScrollDimensions();
+    if (Scrollbar* horizontalScrollbar = this->horizontalScrollbar()) {
+        int clientWidth = m_box.pixelSnappedClientWidth();
+        horizontalScrollbar->setProportion(clientWidth, overflowRect().width());
+    }
+    if (Scrollbar* verticalScrollbar = this->verticalScrollbar()) {
+        int clientHeight = m_box.pixelSnappedClientHeight();
+        verticalScrollbar->setProportion(clientHeight, overflowRect().height());
+    }
+
+    bool hasHorizontalOverflow = this->hasHorizontalOverflow();
+    bool hasVerticalOverflow = this->hasVerticalOverflow();
+    bool autoHorizontalScrollBarChanged = m_box.hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow);
+    bool autoVerticalScrollBarChanged = m_box.hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow);
+    if (autoHorizontalScrollBarChanged || autoVerticalScrollBarChanged)
+        m_box.setNeedsLayout();
+}
+
 IntSize RenderLayerScrollableArea::clampScrollOffset(const IntSize& scrollOffset) const
 {
     int maxX = scrollWidth() - m_box.pixelSnappedClientWidth();