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..3997296bcbc8577f08cb031a6472b9878ce5ab3a 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_horizontalScrollbarChanged(false)
+    , m_verticalScrollbarChanged(false)
     , m_scrollCorner(nullptr)
     , m_resizer(nullptr)
 {
@@ -753,16 +755,35 @@ 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 oldHrect = m_hBar->frameRect();
         m_hBar->styleChanged();
-    if (m_vBar)
+        if ((oldHrect != m_hBar->frameRect()) && m_hBar->isCustomScrollbar())
+            m_horizontalScrollbarChanged = true;
+    }
+    if (m_vBar) {
+        IntRect oldVrect = m_vBar->frameRect();
         m_vBar->styleChanged();
+        if ((oldVrect != m_vBar->frameRect()) && m_vBar->isCustomScrollbar())
+            m_verticalScrollbarChanged = true;
+    }
 
     updateScrollCornerStyle();
     updateResizerAreaSet();
     updateResizerStyle();
 }
 
+bool RenderLayerScrollableArea::didCustomScrollbarRectChanged()
+{
+    bool scrollbarRectChanged = false;
+    if (m_verticalScrollbarChanged || m_horizontalScrollbarChanged) {
+        scrollbarRectChanged = true;
+        m_verticalScrollbarChanged = false;
+        m_horizontalScrollbarChanged = false;
+    }
+    return scrollbarRectChanged;
+}
+
 bool RenderLayerScrollableArea::updateAfterCompositingChange()
 {
     layer()->updateScrollingStateAfterCompositingChange();