Force layout for main thread scrolling.

Source/core/input/EventHandler.cpp

Index: Source/core/input/EventHandler.cpp
diff --git a/Source/core/input/EventHandler.cpp b/Source/core/input/EventHandler.cpp
index 0e66ca528a2bee45a5deb23ea97efac88841b081..19698b6bf5a0b587896378adc6a5058273c8515d 100644
--- a/Source/core/input/EventHandler.cpp
+++ b/Source/core/input/EventHandler.cpp
@@ -561,6 +561,8 @@ ScrollResultOneDimensional EventHandler::scroll(ScrollDirection direction, Scrol
     if (!node || !node->layoutObject())
         return ScrollResultOneDimensional(false, delta);
 
+    m_frame->document()->updateLayoutIgnorePendingStylesheets();
+
     LayoutBox* curBox = node->layoutObject()->enclosingBox();
     while (curBox && !curBox->isLayoutView()) {
         ScrollDirectionPhysical physicalDirection = toPhysicalDirection(
@@ -590,6 +592,9 @@ void EventHandler::customizedScroll(const Node& startNode, ScrollState& scrollSt
     if (scrollState.fullyConsumed())
         return;
 
+    if (scrollState.deltaX() || scrollState.deltaY())
+        m_frame->document()->updateLayoutIgnorePendingStylesheets();
+
     if (m_currentScrollChain.isEmpty())
         recomputeScrollChain(*m_frame, startNode, m_currentScrollChain);
     scrollState.setScrollChain(m_currentScrollChain);