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 54502ea395576daf2d6d81f50626119604972e21..b6966197288d4c19d87b1febe708a4b156851b1f 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_;
 };
 
@@ -373,6 +376,12 @@ void CompositingRequirementsUpdater::UpdateRecursive(
   RecursionData child_recursion_data = current_recursion_data;
   child_recursion_data.subtree_is_compositing_ = false;
 
+  if (layer->SticksToScroller() &&
+      layer->AncestorOverflowLayer()->ScrollsOverflow() &&
+      current_recursion_data.has_composited_non_root_ancestor_) {
+    reasons_to_composite |= kCompositingReasonScrollDependentPosition;

[chrishtr, 2017/05/10 17:48:44]

You don't need current_recursion_data.has_composited_non_root_ancestor_. 

Instead:

if (layer->SticksToScroller() && 
    layer->AncestorScrollingLayer() &&
    current_recursion_data.compositing_ancestor_ &&
// It's actually only needed if the ancestor scrolling layer of
compositing_ancestor_ is below
// the scroller |layer| sticks to, but that is more complicated to compute.
    current_recursion_data.compositing_ancestor_->AncestorScrollingLayer() &&
   
!current_recursion_data.compositing_ancestor_->AncestorScrollingLayer()->IsRoot())
{
  reasons_to_composite |= kCompositingReasonScrollDependentPosition;
}

[yigu, 2017/05/10 18:04:13]

Done.

+  }
+
   bool will_be_composited_or_squashed =
       can_be_composited && RequiresCompositingOrSquashing(reasons_to_composite);
   if (will_be_composited_or_squashed) {
@@ -387,6 +396,10 @@ 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;
   }
 
 #if DCHECK_IS_ON()