Partly revert of Conditionally create PaintLayer's scrollable area object

third_party/WebKit/Source/core/paint/PaintLayer.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 2e2dad8652dfdc483909dd54fe394fa462126c20..4ae5132c89708c12992b47244806223ba351709d 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -1469,14 +1469,9 @@ void PaintLayer::updateStackingNode()
 
 void PaintLayer::updateScrollableArea()
 {
-    if (requiresScrollableArea()) {
-        if (!m_scrollableArea)
-            m_scrollableArea = PaintLayerScrollableArea::create(*this);
-    } else if (m_scrollableArea) {
-        if (m_scrollableArea)
-            m_scrollableArea->dispose();
-        m_scrollableArea.clear();
-    }
+    ASSERT(!m_scrollableArea);
+    if (requiresScrollableArea())
+        m_scrollableArea = PaintLayerScrollableArea::create(*this);
 }
 
 bool PaintLayer::hasOverflowControls() const
@@ -2582,7 +2577,6 @@ void PaintLayer::styleChanged(StyleDifference diff, const ComputedStyle* oldStyl
     m_stackingNode->updateIsTreatedAsStackingContext();
     m_stackingNode->updateStackingNodesAfterStyleChange(oldStyle);
 
-    updateScrollableArea();
     if (m_scrollableArea)
         m_scrollableArea->updateAfterStyleChange(oldStyle);