setNeedsPaintPropertyUpdate on FrameView contents size change

This ensures that the bounds of scroll is updated.

BUG=645667

Review-Url: https://codereview.chromium.org/2545093002
Cr-Commit-Position: refs/heads/master@{#436077}

third_party/WebKit/Source/core/frame/FrameView.cpp

@@ -636,6 +636,10 @@ void FrameView::setContentsSize(const IntSize& size) {
   updateScrollbars();
   ScrollableArea::contentsResized();
 
+  if (RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled() &&
+      !RuntimeEnabledFeatures::rootLayerScrollingEnabled())
+    setNeedsPaintPropertyUpdate();
+
   Page* page = frame().page();
   if (!page)
     return;