[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 997 matching lines @@
   if (NeedsRelayout() && !HadVerticalScrollbarBeforeRelayout())
     client_width += VerticalScrollbarWidth();
   return PixelSnappedScrollWidth() > client_width;
 }
 
 bool PaintLayerScrollableArea::HasVerticalOverflow() const {
   return PixelSnappedScrollHeight() > PixelSnappedClientSize().Height();
 }
 
 bool PaintLayerScrollableArea::HasScrollableHorizontalOverflow() const {
+  if (Box().Size().IsZero())

[skobes, 2017/07/15 00:44:31]

Actually it would be simpler to put this logic inside UpdateScrollableAreaSet,
and remove the has_overflow param.  Then the methods
HasScrollableHorizontalOverflow and HasScrollableVerticalOverflow can be deleted
since they are not used elsewhere.

[Srirama, 2017/07/17 14:35:24]

Done.

+    return false;
+
   return HasHorizontalOverflow() && Box().ScrollsOverflowX();
 }
 
 bool PaintLayerScrollableArea::HasScrollableVerticalOverflow() const {
+  if (Box().Size().IsZero())
+    return false;
+
   return HasVerticalOverflow() && Box().ScrollsOverflowY();
 }
 
 // This function returns true if the given box requires overflow scrollbars (as
 // opposed to the 'viewport' scrollbars managed by the PaintLayerCompositor).
 // FIXME: we should use the same scrolling machinery for both the viewport and
 // overflow. Currently, we need to avoid producing scrollbars here if they'll be
 // handled externally in the RLC.
 static bool CanHaveOverflowScrollbars(const LayoutBox& box) {
   return (RuntimeEnabledFeatures::RootLayerScrollingEnabled() ||
@@ skipping 1228 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollOffsetClampScope::
     ClampScrollableAreas() {
   for (auto& scrollable_area : *needs_clamp_)
     scrollable_area->ClampScrollOffsetAfterOverflowChange();
   delete needs_clamp_;
   needs_clamp_ = nullptr;
 }
 
 }  // namespace blink