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..fccc30d12f46d88386055754c055dd54b208774a 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
@@ -373,6 +373,15 @@ 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.compositing_ancestor_ &&
+      current_recursion_data.compositing_ancestor_->AncestorScrollingLayer() &&

[chrishtr, 2017/05/10 19:29:36]

Please add the comments explaining that this is not exact and over-promotes
sometimes
if compositing_ancestor_ is not under the same scroller as the sticky element.

[yigu, 2017/05/10 20:01:42]

Done.

+      !current_recursion_data.compositing_ancestor_->AncestorScrollingLayer()
+           ->IsRootLayer()) {
+    reasons_to_composite |= kCompositingReasonScrollDependentPosition;
+  }
+
   bool will_be_composited_or_squashed =
       can_be_composited && RequiresCompositingOrSquashing(reasons_to_composite);
   if (will_be_composited_or_squashed) {