RLSA needsLayout on customscrollbar thickness change.

Source/core/rendering/RenderLayerScrollableArea.cpp

Index: Source/core/rendering/RenderLayerScrollableArea.cpp
diff --git a/Source/core/rendering/RenderLayerScrollableArea.cpp b/Source/core/rendering/RenderLayerScrollableArea.cpp
index d61144d26f7814ff6db932f4099e431361ea5cfc..981d1586f6857d2d4596dbb029b15d99adb1b394 100644
--- a/Source/core/rendering/RenderLayerScrollableArea.cpp
+++ b/Source/core/rendering/RenderLayerScrollableArea.cpp
@@ -87,6 +87,8 @@ RenderLayerScrollableArea::RenderLayerScrollableArea(RenderLayer& layer)
     , m_nextTopmostScrollChild(0)
     , m_topmostScrollChild(0)
     , m_needsCompositedScrolling(false)
+    , m_horizontalScrollbarRectChanged(false)
+    , m_verticalScrollbarRectChanged(false)
     , m_scrollCorner(nullptr)
     , m_resizer(nullptr)
 {
@@ -619,10 +621,10 @@ void RenderLayerScrollableArea::updateAfterLayout()
             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())
@@ -637,7 +639,7 @@ void RenderLayerScrollableArea::updateAfterLayout()
         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;
@@ -645,13 +647,15 @@ void RenderLayerScrollableArea::updateAfterLayout()
                 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;
         }
     }
 
@@ -753,10 +757,18 @@ void RenderLayerScrollableArea::updateAfterStyleChange(const RenderStyle* oldSty
     }
 
     // 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();