Delay scrollContents until the next paint

Source/platform/scroll/ScrollView.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 256 matching lines @@
 void ScrollView::scrollTo(const IntSize& newOffset)
 {
     IntSize scrollDelta = newOffset - m_scrollOffset;
     if (scrollDelta == IntSize())
         return;
     m_scrollOffset = newOffset;
 
     if (scrollbarsSuppressed())
         return;
 
-    repaintFixedElementsAfterScrolling();
-    scrollContents(scrollDelta);
-    updateFixedElementsAfterScrolling();
+    m_pendingScrollDelta += scrollDelta;
 }
 
 void ScrollView::setScrollPosition(const IntPoint& scrollPoint)
 {
     IntPoint newScrollPosition = adjustScrollPositionWithinRange(scrollPoint);
 
     if (newScrollPosition == scrollPosition())
         return;
 
     updateScrollbars(IntSize(newScrollPosition.x(), newScrollPosition.y()));
@@ skipping 218 matching lines @@
     if (hasOverlayScrollbars()) {
         int verticalScrollbarWidth = (verticalScrollbar() && !hasLayerForVerticalScrollbar()) ? verticalScrollbar()->width() : 0;
         int horizontalScrollbarHeight = (horizontalScrollbar() && !hasLayerForHorizontalScrollbar()) ? horizontalScrollbar()->height() : 0;
 
         scrollViewRect.setWidth(scrollViewRect.width() - verticalScrollbarWidth);
         scrollViewRect.setHeight(scrollViewRect.height() - horizontalScrollbarHeight);
     }
     return scrollViewRect;
 }
 
+void ScrollView::scrollContentsIfNeeded()
+{
+    if (m_pendingScrollDelta.isZero())
+        return;
+    IntSize scrollDelta = m_pendingScrollDelta;
+    m_pendingScrollDelta = IntSize();
+    scrollContents(scrollDelta);
+}
+
 void ScrollView::scrollContents(const IntSize& scrollDelta)
 {
     HostWindow* window = hostWindow();
     if (!window)
         return;
 
     // Since scrolling is double buffered, we will be blitting the scroll view's intersection
     // with the clip rect every time to keep it smooth.
     IntRect clipRect = windowClipRect();
     IntRect scrollViewRect = rectToCopyOnScroll();
@@ skipping 587 matching lines @@
 int ScrollView::pageStep(ScrollbarOrientation orientation) const
 {
     int length = (orientation == HorizontalScrollbar) ? visibleWidth() : visibleHeight();
     int minPageStep = static_cast<float>(length) * minFractionToStepWhenPaging();
     int pageStep = std::max(minPageStep, length - maxOverlapBetweenPages());
 
     return std::max(pageStep, 1);
 }
 
 } // namespace WebCore