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

third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 254 matching lines @@
   if (current_recursion_data.compositing_ancestor_ &&
       current_recursion_data.compositing_ancestor_->GetLayoutObject().IsVideo())
     direct_reasons |= kCompositingReasonVideoOverlay;
 
   bool has_composited_scrolling_ancestor =
       layer->AncestorScrollingLayer() &&
       (compositing_reason_finder_.DirectReasons(layer->AncestorScrollingLayer(),
                                                 false) &
        kCompositingReasonOverflowScrollingTouch);
 
+  const bool moves_with_respect_to_compositing_ancestor =
+      layer->SticksToScroller();

[flackr, 2017/05/18 18:13:14]

Sorry, can you put both parts of the expression to this calculation here (and
move the comment up)? This moves with respect to compositing ancestor if it has
a non-root compositing ancestor and sticks to scroller.

[yigu, 2017/05/18 19:26:43]

Done.

   // TODO(chrishtr): use |hasCompositedScrollingAncestor| instead.
   const bool ignore_lcd_text =
-      current_recursion_data.has_composited_scrolling_ancestor_;
+      current_recursion_data.has_composited_scrolling_ancestor_ ||
+      // TODO(yigu): We should check if we have already lost lcd text. This
+      // would require tracking if we think the current compositing ancestor
+      // layer meets the requirements (i.e. opaque, integer transform, etc).

[flackr, 2017/05/18 18:13:14]

From your discussions with Chris, we also have to promote right now to work
around a bug of not being able to invalidate the ancestor after updating the
sticky layer position, right? (can you add this to the comment).

[yigu, 2017/05/18 19:26:43]

Done.

+      (moves_with_respect_to_compositing_ancestor &&
+       !current_recursion_data.compositing_ancestor_->IsRootLayer());
   direct_reasons |=
       compositing_reason_finder_.DirectReasons(layer, ignore_lcd_text);
 
   bool can_be_composited = compositor->CanBeComposited(layer);
   if (can_be_composited) {
     reasons_to_composite |= direct_reasons;
 
     if (layer->IsRootLayer() && compositor->RootShouldAlwaysComposite())
       reasons_to_composite |= kCompositingReasonRoot;
 
@@ skipping 268 matching lines @@
     descendant_has3d_transform |=
         any_descendant_has3d_transform || layer->Has3DTransform();
   }
 
   // At this point we have finished collecting all reasons to composite this
   // layer.
   layer->SetCompositingReasons(reasons_to_composite);
 }
 
 }  // namespace blink