RLSA needsLayout on customscrollbar thickness change.

Source/core/rendering/RenderLayerScrollableArea.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 69 matching lines @@
 
 RenderLayerScrollableArea::RenderLayerScrollableArea(RenderLayer& layer)
     : m_layer(layer)
     , m_inResizeMode(false)
     , m_scrollsOverflow(false)
     , m_scrollDimensionsDirty(true)
     , m_inOverflowRelayout(false)
     , m_nextTopmostScrollChild(0)
     , m_topmostScrollChild(0)
     , m_needsCompositedScrolling(false)
+    , m_horizontalScrollbarRectChanged(false)
+    , m_verticalScrollbarRectChanged(false)
     , m_scrollCorner(nullptr)
     , m_resizer(nullptr)
 {
     ScrollableArea::setConstrainsScrollingToContentEdge(false);
 
     Node* node = box().node();
     if (node && node->isElementNode()) {
         // We save and restore only the scrollOffset as the other scroll values are recalculated.
         Element* element = toElement(node);
         m_scrollOffset = element->savedLayerScrollOffset();
@@ skipping 512 matching lines @@
         if (box().style()->overflowY() == OSCROLL && verticalScrollbar())
             verticalScrollbar()->setEnabled(hasVerticalOverflow);
     }
     if (hasOverlayScrollbars()) {
         if (!scrollSize(HorizontalScrollbar))
             setHasHorizontalScrollbar(false);
         if (!scrollSize(VerticalScrollbar))
             setHasVerticalScrollbar(false);
     }
     // overflow:auto may need to lay out again if scrollbars got added/removed.
-    bool autoHorizontalScrollBarChanged = box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow);
-    bool autoVerticalScrollBarChanged = box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow);
+    bool horizontalScrollBarChanged = (box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow)) || m_horizontalScrollbarRectChanged;
+    bool verticalScrollBarChanged = (box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow)) || m_verticalScrollbarRectChanged;
 
-    if (autoHorizontalScrollBarChanged || autoVerticalScrollBarChanged) {
+    if (horizontalScrollBarChanged || verticalScrollBarChanged) {
         if (box().hasAutoHorizontalScrollbar())
             setHasHorizontalScrollbar(hasHorizontalOverflow);
         if (box().hasAutoVerticalScrollbar())
             setHasVerticalScrollbar(hasVerticalOverflow);
 
         if (hasVerticalOverflow || hasHorizontalOverflow)
             updateScrollCornerStyle();
 
         layer()->updateSelfPaintingLayer();
 
         // 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 (box().style()->overflowX() == OAUTO || box().style()->overflowY() == OAUTO || m_verticalScrollbarRectChanged || m_horizontalScrollbarRectChanged) {

[skobes, 2014/11/10 20:26:09]

I think this codepath is intended for the case where we need a second layout
because the first layout caused a scrollbar to be added or removed.  But for a
change in scrollbar style, we don't need a second layout; the normal layout
should handle it.

Instead, updateAfterStyleChange should just mark the box as needing layout, if
the scrollbar frame rect has changed.  Can you see if that fixes the issue?

             if (!m_inOverflowRelayout) {
                 // Our proprietary overflow: overlay value doesn't trigger a layout.
                 m_inOverflowRelayout = true;
                 SubtreeLayoutScope layoutScope(box());
                 layoutScope.setNeedsLayout(&box());
                 if (box().isRenderBlock()) {
                     RenderBlock& block = toRenderBlock(box());
-                    block.scrollbarsChanged(autoHorizontalScrollBarChanged, autoVerticalScrollBarChanged);
+                    block.scrollbarsChanged(horizontalScrollBarChanged, verticalScrollBarChanged);
                     block.layoutBlock(true);
                 } else {
                     box().layout();
                 }
                 m_inOverflowRelayout = false;
             }
+            m_verticalScrollbarRectChanged = false;
+            m_horizontalScrollbarRectChanged = false;
         }
     }
 
     {
         // Hits in compositing/overflow/automatically-opt-into-composited-scrolling-after-style-change.html.
         DisableCompositingQueryAsserts disabler;
 
         // Set up the range (and page step/line step).
         if (Scrollbar* horizontalScrollbar = this->horizontalScrollbar()) {
             int clientWidth = box().pixelSnappedClientWidth();
@@ skipping 81 matching lines @@
         ASSERT(hasHorizontalScrollbar());
         m_hBar->setEnabled(true);
     }
 
     if (needsVerticalScrollbar && oldStyle && oldStyle->overflowY() == OSCROLL && overflowY != OSCROLL) {
         ASSERT(hasVerticalScrollbar());
         m_vBar->setEnabled(true);
     }
 
     // FIXME: Need to detect a swap from custom to native scrollbars (and vice versa).
-    if (m_hBar)
+    if (m_hBar) {
+        IntRect oldHBarRect = m_hBar->frameRect();
         m_hBar->styleChanged();
-    if (m_vBar)
+        if (oldHBarRect != m_hBar->frameRect())
+            m_horizontalScrollbarRectChanged = true;
+    }
+    if (m_vBar) {
+        IntRect oldVBarRect = m_vBar->frameRect();
         m_vBar->styleChanged();
+        if (oldVBarRect != m_vBar->frameRect())
+            m_verticalScrollbarRectChanged = true;
+    }
 

[MuVen, 2014/11/11 14:45:04]

    if (box().isRenderBlock()) {
        RenderBlock& block = toRenderBlock(box());
        block.scrollbarsChanged(m_horizontalScrollbarRectChanged,
m_verticalScrollbarRectChanged);
        block.setNeedsLayout();
    } else {
        box().setNeedsLayout();
    }

I have tried earlier with above snippet, but i still see the issue. This
provoked me to go for force layout.

     updateScrollCornerStyle();
     updateResizerAreaSet();
     updateResizerStyle();
 }
 
 bool RenderLayerScrollableArea::updateAfterCompositingChange()
 {
     layer()->updateScrollingStateAfterCompositingChange();
     const bool layersChanged = m_topmostScrollChild != m_nextTopmostScrollChild;
     m_topmostScrollChild = m_nextTopmostScrollChild;
@@ skipping 717 matching lines @@
 void RenderLayerScrollableArea::setTopmostScrollChild(RenderLayer* scrollChild)
 {
     // We only want to track the topmost scroll child for scrollable areas with
     // overlay scrollbars.
     if (!hasOverlayScrollbars())
         return;
     m_nextTopmostScrollChild = scrollChild;
 }
 
 } // namespace blink