Refactor scroll updates during flexbox layout.

third_party/WebKit/Source/core/layout/LayoutFlexibleBox.cpp

 /*
  * Copyright (C) 2011 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 318 matching lines @@
 
     m_relaidOutChildren.clear();
 
     if (updateLogicalWidthAndColumnWidth())
         relayoutChildren = true;
 
     SubtreeLayoutScope layoutScope(*this);
     LayoutUnit previousHeight = logicalHeight();
     setLogicalHeight(borderAndPaddingLogicalHeight() + scrollbarLogicalHeight());
 
+    PaintLayerScrollableArea::DelayScrollPositionClampScope delayClampScope;
+
     {
         TextAutosizer::LayoutScope textAutosizerLayoutScope(this, &layoutScope);
         LayoutState state(*this, locationOffset());
 
         m_numberOfInFlowChildrenOnFirstLine = -1;
 
-        LayoutBlock::startDelayUpdateScrollInfo();
-
         prepareOrderIteratorAndMargins();
 
         layoutFlexItems(relayoutChildren, layoutScope);
-
-        ScrollPositionMap scrollMap;
-        if (LayoutBlock::finishDelayUpdateScrollInfo(&layoutScope, &scrollMap)) {
+        if (PaintLayerScrollableArea::PreventRelayoutScope::relayoutNeeded()) {
+            PaintLayerScrollableArea::FreezeScrollbarsScope freezeScrollbarsScope;
             prepareOrderIteratorAndMargins();
-            layoutFlexItems(false, layoutScope);
-            for (auto& entry : scrollMap) {
-                entry.key->scrollToPosition(entry.value, ScrollOffsetClamped);
-            }
+            layoutFlexItems(true, layoutScope);
+            PaintLayerScrollableArea::PreventRelayoutScope::resetRelayoutNeeded();
         }
 
         if (logicalHeight() != previousHeight)
             relayoutChildren = true;
 
         layoutPositionedObjects(relayoutChildren || isDocumentElement());
 
         // FIXME: css3/flexbox/repaint-rtl-column.html seems to issue paint invalidations for more overflow than it needs to.
         computeOverflow(clientLogicalBottomAfterRepositioning());
     }
@@ skipping 476 matching lines @@
     Vector<LineContext> lineContexts;
     OrderedFlexItemList orderedChildren;
     LayoutUnit sumFlexBaseSize;
     double totalFlexGrow;
     double totalFlexShrink;
     double totalWeightedFlexShrink;
     LayoutUnit sumHypotheticalMainSize;
 
     Vector<LayoutUnit, 16> childSizes;
 
+    PaintLayerScrollableArea::PreventRelayoutScope preventRelayoutScope(layoutScope);
+
     dirtyForLayoutFromPercentageHeightDescendants(layoutScope);
 
     m_orderIterator.first();
     LayoutUnit crossAxisOffset = flowAwareBorderBefore() + flowAwarePaddingBefore();
     while (computeNextFlexLine(orderedChildren, sumFlexBaseSize, totalFlexGrow, totalFlexShrink, totalWeightedFlexShrink, sumHypotheticalMainSize, relayoutChildren)) {
         LayoutUnit containerMainInnerSize = mainAxisContentExtent(sumHypotheticalMainSize);
         // availableFreeSpace is the initial amount of free space in this flexbox.
         // remainingFreeSpace starts out at the same value but as we place and lay out
         // flex items we subtract from it. Note that both values can be negative.
         const LayoutUnit availableFreeSpace = containerMainInnerSize - sumFlexBaseSize;
@@ skipping 998 matching lines @@
             ASSERT(child);
             LayoutUnit lineCrossAxisExtent = lineContexts[lineNumber].crossAxisExtent;
             LayoutUnit originalOffset = lineContexts[lineNumber].crossAxisOffset - crossAxisStartEdge;
             LayoutUnit newOffset = contentExtent - originalOffset - lineCrossAxisExtent;
             adjustAlignmentForChild(*child, newOffset - originalOffset);
         }
     }
 }
 
 } // namespace blink