Reland of 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 14086dc9317f532ec5a0990aaaec68201984456a..5b9880da1de221909a6418e50b6d87150edbf9a0 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
@@ -406,21 +406,11 @@
 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;