Fix several corner case issues of scrollbar paint invalidation

third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
index 85016be74b5a15c2f326a65e4254a439ceac12f6..3b6d588462e422ff844f0478f12723a6c90caa4b 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
@@ -407,21 +407,11 @@ void ScrollableArea::setScrollbarOverlayStyle(ScrollbarOverlayStyle overlayStyle
 void ScrollableArea::setScrollbarNeedsPaintInvalidation(Scrollbar* scrollbar)
 {
     if (scrollbar == horizontalScrollbar()) {
-        if (GraphicsLayer* graphicsLayer = layerForHorizontalScrollbar()) {
-            graphicsLayer->setNeedsDisplay();
-            graphicsLayer->setContentsNeedsDisplay();
-            return;
-        }
         m_horizontalScrollbarNeedsPaintInvalidation = true;
         scrollControlWasSetNeedsPaintInvalidation();
         return;
     }
     if (scrollbar == verticalScrollbar()) {
-        if (GraphicsLayer* graphicsLayer = layerForVerticalScrollbar()) {
-            graphicsLayer->setNeedsDisplay();
-            graphicsLayer->setContentsNeedsDisplay();
-            return;
-        }
         m_verticalScrollbarNeedsPaintInvalidation = true;
         scrollControlWasSetNeedsPaintInvalidation();
         return;