Begin tracking why layout is invalidated

Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 677 matching lines @@
 
         // Force an update since we know the scrollbars have changed things.
         if (box().document().hasAnnotatedRegions())
             box().document().setAnnotatedRegionsDirty(true);
 
         if (box().style()->overflowX() == OAUTO || box().style()->overflowY() == OAUTO) {
             if (!m_inOverflowRelayout) {
                 // Our proprietary overflow: overlay value doesn't trigger a layout.
                 m_inOverflowRelayout = true;
                 SubtreeLayoutScope layoutScope(box());
-                layoutScope.setNeedsLayout(&box());
+                layoutScope.setNeedsLayout(&box(), LayoutInvalidationReason::ScrollbarChanged);
                 if (box().isLayoutBlock()) {
                     LayoutBlock& block = toLayoutBlock(box());
                     block.scrollbarsChanged(autoHorizontalScrollBarChanged, autoVerticalScrollBarChanged);
                     block.layoutBlock(true);
                 } else {
                     box().layout();
                 }
                 m_inOverflowRelayout = false;
             }
         }
@@ skipping 125 matching lines @@
     if (Scrollbar* verticalScrollbar = this->verticalScrollbar()) {
         int clientHeight = box().pixelSnappedClientHeight();
         verticalScrollbar->setProportion(clientHeight, overflowRect().height());
     }
 
     bool hasHorizontalOverflow = this->hasHorizontalOverflow();
     bool hasVerticalOverflow = this->hasVerticalOverflow();
     bool autoHorizontalScrollBarChanged = box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow);
     bool autoVerticalScrollBarChanged = box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow);
     if (autoHorizontalScrollBarChanged || autoVerticalScrollBarChanged)
-        box().setNeedsLayoutAndFullPaintInvalidation();
+        box().setNeedsLayoutAndFullPaintInvalidation(LayoutInvalidationReason::Unknown);
 }
 
 DoubleSize DeprecatedPaintLayerScrollableArea::clampScrollOffset(const DoubleSize& scrollOffset) const
 {
     int maxX = scrollWidth() - box().pixelSnappedClientWidth();
     int maxY = scrollHeight() - box().pixelSnappedClientHeight();
 
     double x = std::max(std::min(scrollOffset.width(), static_cast<double>(maxX)), 0.0);
     double y = std::max(std::min(scrollOffset.height(), static_cast<double>(maxY)), 0.0);
     return DoubleSize(x, y);
@@ skipping 531 matching lines @@
 void DeprecatedPaintLayerScrollableArea::setTopmostScrollChild(DeprecatedPaintLayer* scrollChild)
 {
     // We only want to track the topmost scroll child for scrollable areas with
     // overlay scrollbars.
     if (!hasOverlayScrollbars())
         return;
     m_nextTopmostScrollChild = scrollChild;
 }
 
 } // namespace blink