[RLS] Don't add to ScrollableAreaSet if the size is zero

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@gmail.com>
@@ skipping 1759 matching lines @@
   scrolls_overflow_ = has_overflow && is_visible_to_hit_test;
   if (did_scroll_overflow == ScrollsOverflow())
     return;
 
   if (RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled()) {
     // The scroll and scroll offset properties depend on |scrollsOverflow| (see:
     // PaintPropertyTreeBuilder::updateScrollAndScrollTranslation).
     Box().SetNeedsPaintPropertyUpdate();
   }
 
-  if (scrolls_overflow_) {
+  if (scrolls_overflow_ && frame_view->IsScrollable()) {

[Srirama, 2017/05/05 06:21:22]

IsScrollable is calling GetScrollingReasons and that internally checks for 4
conditions. I think what is missing here is the first condition (If there is an
actual overflow). Ideally adding the first condition alone here should work but
it is not. Incase of NO-RLS flow contents_size is coming {0, 0} where as in RLS
flow, contents_size is coming as {1, 8}. So i think we need to debug more to
find out how size is coming as {1, 8}.

     DCHECK(CanHaveOverflowScrollbars(Box()));
     frame_view->AddScrollableArea(this);
   } else {
     frame_view->RemoveScrollableArea(this);
   }
 }
 
 void PaintLayerScrollableArea::UpdateCompositingLayersAfterScroll() {
   PaintLayerCompositor* compositor = Box().View()->Compositor();
   if (compositor->InCompositingMode()) {
@@ skipping 386 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollOffsetClampScope::
     ClampScrollableAreas() {
   for (auto& scrollable_area : *needs_clamp_)
     scrollable_area->ClampScrollOffsetAfterOverflowChange();
   delete needs_clamp_;
   needs_clamp_ = nullptr;
 }
 
 }  // namespace blink