Fix the bug that sticky element may not be correctly invalidated due to non-promotion

third_party/WebKit/Source/core/paint/PaintLayer.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@web.de>
@@ skipping 820 matching lines @@
       // Adjust offset for absolute under in-flow positioned inline.
       LayoutSize offset =
           ToLayoutInline(containing_layer->GetLayoutObject())
               .OffsetForInFlowPositionedInline(ToLayoutBox(GetLayoutObject()));
       local_point += offset;
     }
   }
 
   if (GetLayoutObject().IsInFlowPositioned()) {
     LayoutSize new_offset = GetLayoutObject().OffsetForInFlowPosition();
+    if (!HasCompositedLayerMapping() &&

[chrishtr, 2017/04/28 20:11:43]

This is not in general the right place to be doing paint invalidations like
this.
But maybe there is something new to add...could you explain the core issue
thatis happening in these cases? I'm not yet sure what it is.

Please also update the title of the patch to match the description of the core
issue.

[yigu, 2017/04/28 20:38:56]

Suppose we have a region A that needs repaint on scroll and it has a composited
but main thread scrolled child B. When we recursively do paint invalidation from
A we may stop at the composited child B so B's non-composited children cannot
get invalidated. Here we invalidate the children if their location changed.

+        OffsetForInFlowPosition() != new_offset) {
+      GetLayoutObject().SetShouldDoFullPaintInvalidation(
+          kPaintInvalidationLocationChange);
+    }
     if (rare_data_ || !new_offset.IsZero())
       EnsureRareData().offset_for_in_flow_position = new_offset;
     local_point.Move(new_offset);
   } else if (rare_data_) {
     rare_data_->offset_for_in_flow_position = LayoutSize();
   }
 
   location_ = local_point;
 
   if (scrollable_area_ && did_resize)
@@ skipping 2466 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->EnclosingLayer());
 }
 #endif