Revert of Calculate paint invalidation rect for scrollbars

third_party/WebKit/Source/core/layout/LayoutScrollbar.cpp

Index: third_party/WebKit/Source/core/layout/LayoutScrollbar.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutScrollbar.cpp b/third_party/WebKit/Source/core/layout/LayoutScrollbar.cpp
index f3016e76d1c3dcd71d0d22c6a0b8194fa6b0f6e7..ec94233154d2528f740ea3e93e6c53e085d67b39 100644
--- a/third_party/WebKit/Source/core/layout/LayoutScrollbar.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutScrollbar.cpp
@@ -201,7 +201,7 @@
                 toLayoutBlock(box)->notifyScrollbarThicknessChanged();
             box->setChildNeedsLayout();
             if (m_scrollableArea)
-                m_scrollableArea->setScrollCornerNeedsPaintInvalidation();
+                m_scrollableArea->invalidateScrollCorner(m_scrollableArea->scrollCornerRect());
         }
     }
 }
@@ -362,10 +362,15 @@
     return orientation() == HorizontalScrollbar ? partLayoutObject->size().width() : partLayoutObject->size().height();
 }
 
-void LayoutScrollbar::invalidateDisplayItemClientsOfScrollbarParts(const LayoutBoxModelObject& paintInvalidationContainer, const LayoutRect& paintInvalidationRect)
-{
-    for (auto& part : m_parts)
-        part.value->invalidateDisplayItemClientsIncludingNonCompositingDescendants(&paintInvalidationContainer, PaintInvalidationScroll, &paintInvalidationRect);
-}
-
-}
+void LayoutScrollbar::invalidateRect(const IntRect& rect)
+{
+    Scrollbar::invalidateRect(rect);
+
+    // FIXME: invalidate only the changed part.
+    if (LayoutBox* owningLayoutObject = this->owningLayoutObject()) {
+        for (auto& part : m_parts)
+            owningLayoutObject->invalidateDisplayItemClientForNonCompositingDescendantsOf(*part.value);
+    }
+}
+
+}