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 129 matching lines @@
   Vector<OverlapMapContainers> overlap_stack_;
 };
 
 class CompositingRequirementsUpdater::RecursionData {
  public:
   explicit RecursionData(PaintLayer* compositing_ancestor)
       : compositing_ancestor_(compositing_ancestor),
         subtree_is_compositing_(false),
         has_unisolated_composited_blending_descendant_(false),
         testing_overlap_(true),
+        has_composited_non_root_ancestor_(false),
         has_composited_scrolling_ancestor_(false) {}
 
   PaintLayer* compositing_ancestor_;
   bool subtree_is_compositing_;
   bool has_unisolated_composited_blending_descendant_;
   bool testing_overlap_;
+  // Ancestors may be composited but not have composited scrolling layer.
+  bool has_composited_non_root_ancestor_;
   bool has_composited_scrolling_ancestor_;
 };
 
 static bool RequiresCompositingOrSquashing(CompositingReasons reasons) {
 #if DCHECK_IS_ON()
   bool fast_answer = reasons != kCompositingReasonNone;
   bool slow_answer = RequiresCompositing(reasons) || RequiresSquashing(reasons);
   DCHECK_EQ(slow_answer, fast_answer);
 #endif
   return reasons != kCompositingReasonNone;
@@ skipping 101 matching lines @@
     direct_reasons |= kCompositingReasonVideoOverlay;
 
   bool has_composited_scrolling_ancestor =
       layer->AncestorScrollingLayer() &&
       (compositing_reason_finder_.DirectReasons(layer->AncestorScrollingLayer(),
                                                 false) &
        kCompositingReasonOverflowScrollingTouch);
 
   // TODO(chrishtr): use |hasCompositedScrollingAncestor| instead.
   const bool ignore_lcd_text =
-      current_recursion_data.has_composited_scrolling_ancestor_;
+      current_recursion_data.has_composited_scrolling_ancestor_ ||
+      (layer->SticksToScroller() &&

[flackr, 2017/05/17 20:18:57]

For clarity, can you calculate a named local bool for this, i.e.
bool moves_with_respect_to_compositing_ancestor = ...

It seems like we should really be checking 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). Add a TODO for
this.

[yigu, 2017/05/18 18:00:35]

Done.

+       current_recursion_data.has_composited_non_root_ancestor_);
   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 91 matching lines @@
     child_recursion_data.compositing_ancestor_ = layer;
 
     // Here we know that all children and the layer's own contents can blindly
     // paint into this layer's backing, until a descendant is composited. So, we
     // don't need to check for overlap with anything behind this layer.
     overlap_map.BeginNewOverlapTestingContext();
     // This layer is going to be composited, so children can safely ignore the
     // fact that there's an animation running behind this layer, meaning they
     // can rely on the overlap map testing again.
     child_recursion_data.testing_overlap_ = true;
+
+    // Tell the descendants they have composited non-root ancestor.
+    if (!layer->IsRootLayer())
+      child_recursion_data.has_composited_non_root_ancestor_ = true;

[flackr, 2017/05/17 20:18:57]

Couldn't we determine this by checking
!child_recursion_data.compositing_ancestor_->IsRootLayer()?

[yigu, 2017/05/18 18:00:35]

Done.

   }
 
 #if DCHECK_IS_ON()
   LayerListMutationDetector mutation_checker(layer->StackingNode());
 #endif
 
   bool any_descendant_has3d_transform = false;
   bool will_have_foreground_layer = false;
 
   if (layer->StackingNode()->IsStackingContext()) {
@@ skipping 157 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