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

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

Index: third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
index 43d57ebe4b042d11783e96ac70281c34fc84ca55..9286c96e1d93615e5853f7acddb1bcf26ed84250 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
@@ -147,12 +147,15 @@ class CompositingRequirementsUpdater::RecursionData {
         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_;
 };
 
@@ -274,7 +277,9 @@ void CompositingRequirementsUpdater::UpdateRecursive(
 
   // 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);
 
@@ -386,6 +391,10 @@ void CompositingRequirementsUpdater::UpdateRecursive(
     // 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()