Don't invalidate width for children unless scrollbars have changed.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.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@gmail.com>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 69 matching lines @@
 namespace blink {
 
 PaintLayerScrollableAreaRareData::PaintLayerScrollableAreaRareData()
 {
 }
 
 const int ResizerControlExpandRatioForTouch = 2;
 
 PaintLayerScrollableArea::PaintLayerScrollableArea(PaintLayer& layer)
     : m_layer(layer)
+    , m_nextTopmostScrollChild(0)
+    , m_topmostScrollChild(0)
     , m_inResizeMode(false)
     , m_scrollsOverflow(false)
     , m_inOverflowRelayout(false)
-    , m_nextTopmostScrollChild(0)
-    , m_topmostScrollChild(0)
     , m_needsCompositedScrolling(false)
     , m_rebuildHorizontalScrollbarLayer(false)
     , m_rebuildVerticalScrollbarLayer(false)
+    , m_needsScrollPositionClamp(false)
+    , m_needsRelayout(false)
+    , m_hadHorizontalScrollbarBeforeRelayout(false)
+    , m_hadVerticalScrollbarBeforeRelayout(false)
     , m_scrollbarManager(*this)
     , m_scrollCorner(nullptr)
     , m_resizer(nullptr)
     , m_scrollAnchor(this)
 #if ENABLE(ASSERT)
     , m_hasBeenDisposed(false)
 #endif
 {
     Node* node = box().node();
     if (node && node->isElementNode()) {
@@ skipping 540 matching lines @@
     // We need to layout again if scrollbars are added or removed by overflow:auto,
     // or by changing between native and custom.
     bool horizontalScrollbarShouldChange = (box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != shouldHaveAutoHorizontalScrollbar))
         || (box().style()->overflowX() == OverflowScroll && !horizontalScrollbar());
     bool verticalScrollbarShouldChange = (box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != shouldHaveAutoVerticalScrollbar))
         || (box().style()->overflowY() == OverflowScroll && !verticalScrollbar());
     bool scrollbarsWillChange = !scrollbarsAreFrozen && !visualViewportSuppliesScrollbars()
         && (horizontalScrollbarShouldChange || verticalScrollbarShouldChange);
 
     if (scrollbarsWillChange) {
+        bool hadHorizontalScrollbar = hasHorizontalScrollbar();
+        bool hadVerticalScrollbar = hasVerticalScrollbar();
         if (box().hasAutoHorizontalScrollbar())
             setHasHorizontalScrollbar(shouldHaveAutoHorizontalScrollbar);
         else if (box().style()->overflowX() == OverflowScroll)
             setHasHorizontalScrollbar(true);
         if (box().hasAutoVerticalScrollbar())
             setHasVerticalScrollbar(shouldHaveAutoVerticalScrollbar);
         else if (box().style()->overflowY() == OverflowScroll)
             setHasVerticalScrollbar(true);
 
         if (hasScrollbar())
             updateScrollCornerStyle();
 
         layer()->updateSelfPaintingLayer();
 
         // Force an update since we know the scrollbars have changed things.
         if (box().document().hasAnnotatedRegions())
             box().document().setAnnotatedRegionsDirty(true);
 
         // Our proprietary overflow: overlay value doesn't trigger a layout.
         if ((horizontalScrollbarShouldChange && box().style()->overflowX() != OverflowOverlay)
             || (verticalScrollbarShouldChange && box().style()->overflowY() != OverflowOverlay)) {
             if ((verticalScrollbarShouldChange && box().isHorizontalWritingMode())
                 || (horizontalScrollbarShouldChange && !box().isHorizontalWritingMode())) {
                 box().setPreferredLogicalWidthsDirty();
             }
             if (relayoutIsPrevented) {
                 // We're not doing re-layout right now, but we still want to
                 // add the scrollbar to the logical width now, to facilitate parent layout.
                 box().updateLogicalWidth();
-                if (box().isLayoutBlock())
-                    toLayoutBlock(box()).scrollbarsChanged(horizontalScrollbarShouldChange, verticalScrollbarShouldChange);
-                PreventRelayoutScope::setNeedsLayout(box());
+                PreventRelayoutScope::setBoxNeedsLayout(*this, hadHorizontalScrollbar, hadVerticalScrollbar);
             } else {
                 m_inOverflowRelayout = true;
                 SubtreeLayoutScope layoutScope(box());
                 layoutScope.setNeedsLayout(&box(), LayoutInvalidationReason::ScrollbarChanged);
                 if (box().isLayoutBlock()) {
                     LayoutBlock& block = toLayoutBlock(box());
                     block.scrollbarsChanged(horizontalScrollbarShouldChange, verticalScrollbarShouldChange);
                     block.layoutBlock(true);
                 } else {
                     box().layout();
@@ skipping 939 matching lines @@
 DEFINE_TRACE(PaintLayerScrollableArea::ScrollbarManager)
 {
     visitor->trace(m_scrollableArea);
     visitor->trace(m_hBar);
     visitor->trace(m_vBar);
 }
 
 int PaintLayerScrollableArea::PreventRelayoutScope::s_count = 0;
 SubtreeLayoutScope* PaintLayerScrollableArea::PreventRelayoutScope::s_layoutScope = nullptr;
 bool PaintLayerScrollableArea::PreventRelayoutScope::s_relayoutNeeded = false;
-WTF::Vector<LayoutObject*>* PaintLayerScrollableArea::PreventRelayoutScope::s_needsRelayout = nullptr;
+PersistentHeapVector<Member<PaintLayerScrollableArea>>* PaintLayerScrollableArea::PreventRelayoutScope::s_needsRelayout = nullptr;
 
 PaintLayerScrollableArea::PreventRelayoutScope::PreventRelayoutScope(SubtreeLayoutScope& layoutScope)
 {
     if (!s_count) {
         DCHECK(!s_layoutScope);
         DCHECK(!s_needsRelayout || s_needsRelayout->isEmpty());
         s_layoutScope = &layoutScope;
     }
     s_count++;
 }
 
 PaintLayerScrollableArea::PreventRelayoutScope::~PreventRelayoutScope()
 {
     if (--s_count == 0) {
         if (s_relayoutNeeded) {
-            for (auto layoutObject : *s_needsRelayout)
-                s_layoutScope->setNeedsLayout(layoutObject, LayoutInvalidationReason::ScrollbarChanged);
+            for (auto scrollableArea: *s_needsRelayout) {
+                DCHECK(scrollableArea->needsRelayout());
+                LayoutBox& box = scrollableArea->box();
+                s_layoutScope->setNeedsLayout(&box, LayoutInvalidationReason::ScrollbarChanged);
+                if (box.isLayoutBlock()) {
+                    bool horizontalScrollbarChanged = scrollableArea->hasHorizontalScrollbar() != scrollableArea->hadHorizontalScrollbarBeforeRelayout();
+                    bool verticalScrollbarChanged = scrollableArea->hasVerticalScrollbar() != scrollableArea->hadVerticalScrollbarBeforeRelayout();
+                    if (horizontalScrollbarChanged || verticalScrollbarChanged)
+                        toLayoutBlock(box).scrollbarsChanged(horizontalScrollbarChanged, verticalScrollbarChanged);
+                }
+                scrollableArea->setNeedsRelayout(false);
+            }
+
             s_needsRelayout->clear();
         }
         s_layoutScope = nullptr;
     }
 }
 
-void PaintLayerScrollableArea::PreventRelayoutScope::setNeedsLayout(LayoutObject& layoutObject)
+void PaintLayerScrollableArea::PreventRelayoutScope::setBoxNeedsLayout(PaintLayerScrollableArea& scrollableArea, bool hadHorizontalScrollbar, bool hadVerticalScrollbar)
 {
     DCHECK(s_count);
     DCHECK(s_layoutScope);
+    if (scrollableArea.needsRelayout())
+        return;
+    scrollableArea.setNeedsRelayout(true);
+    scrollableArea.setHadHorizontalScrollbarBeforeRelayout(hadHorizontalScrollbar);
+    scrollableArea.setHadVerticalScrollbarBeforeRelayout(hadVerticalScrollbar);
+
     s_relayoutNeeded = true;
     if (!s_needsRelayout)
-        s_needsRelayout = new WTF::Vector<LayoutObject*>();
-    s_needsRelayout->append(&layoutObject);
+        s_needsRelayout = new PersistentHeapVector<Member<PaintLayerScrollableArea>>();
+    s_needsRelayout->append(&scrollableArea);
 }
 
 void PaintLayerScrollableArea::PreventRelayoutScope::resetRelayoutNeeded()
 {
     DCHECK_EQ(s_count, 0);
     DCHECK(!s_needsRelayout || s_needsRelayout->isEmpty());
     s_relayoutNeeded = false;
 }
 
 int PaintLayerScrollableArea::FreezeScrollbarsScope::s_count = 0;
@@ skipping 25 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollPositionClampScope::clampScrollableAreas()
 {
     for (auto& scrollableArea : *s_needsClamp)
         scrollableArea->clampScrollPositionsAfterLayout();
     delete s_needsClamp;
     s_needsClamp = nullptr;
 }
 
 } // namespace blink