Invalidate scrolling contents layer on background invalidations painted into it.

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

Index: third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
index 3ea4a8860e85050dcc59996cc8ac3300c77f712a..1bd4a34160cb5ff40f4a267aa61d28c767f9d78a 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
@@ -434,6 +434,12 @@ void LayoutBoxModelObject::setBackingNeedsPaintInvalidationInRect(const LayoutRe
     } else if (object.compositedScrollsWithRespectTo(*this)) {
         layer()->compositedLayerMapping()->setScrollingContentsNeedDisplayInRect(r, invalidationReason, object);
     } else if (usesCompositedScrolling()) {
+        if (layer()->compositedLayerMapping()->shouldPaintBackgroundOntoScrollingContentsLayer()) {
+            // TODO(flackr): Get a correct rect in the context of the scrolling contents layer to update
+            // rather than updating the entire rect.
+            const LayoutRect& scrollingContentsRect = toLayoutBox(this)->layoutOverflowRect();
+            layer()->compositedLayerMapping()->setScrollingContentsNeedDisplayInRect(scrollingContentsRect, invalidationReason, object);
+        }
         layer()->compositedLayerMapping()->setNonScrollingContentsNeedDisplayInRect(r, invalidationReason, object);
     } else {
         // Otherwise invalidate everything.