Fix several corner case issues of scrollbar paint invalidation

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

Index: third_party/WebKit/Source/core/layout/LayoutObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.cpp b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
index 21e6e9cd7f463c54dd4d7ea778c4bf3770bf49ad..ea56d1dcf3c2bdc8ba255b17d50ff66c6f053381 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -1522,6 +1522,11 @@ void LayoutObject::adjustPreviousPaintInvalidationForScrollIfNeeded(const Double
     m_previousPaintInvalidationRect.move(LayoutSize(scrollDelta));
 }
 
+void LayoutObject::clearPreviousPaintInvalidationRects()
+{
+    setPreviousPaintInvalidationRect(LayoutRect());
+}
+
 void LayoutObject::incrementallyInvalidatePaint(const LayoutBoxModelObject& paintInvalidationContainer, const LayoutRect& oldBounds, const LayoutRect& newBounds, const LayoutPoint& positionFromPaintInvalidationBacking)
 {
     ASSERT(oldBounds.location() == newBounds.location());
@@ -3407,7 +3412,7 @@ void LayoutObject::invalidatePaintOfPreviousPaintInvalidationRect(const LayoutBo
     // Clear previous paint invalidation rect on the original paint invalidation container to avoid
     // under-invalidation if the new paint invalidation rect on the new paint invalidation container
     // happens to be the same as the old one.
-    setPreviousPaintInvalidationRect(LayoutRect());
+    clearPreviousPaintInvalidationRects();
 }
 
 void LayoutObject::invalidatePaintIncludingNonCompositingDescendants()