Composite sticky-positioned elements when they have composited descendants

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 617d570621a6d956d6561ac1812f287b02760740..955411e1ba9edc27c0cc34af55079816a4e9935f 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
@@ -166,6 +166,7 @@ static bool RequiresCompositingOrSquashing(CompositingReasons reasons) {
 }
 
 static CompositingReasons SubtreeReasonsForCompositing(
+    const CompositingReasonFinder& compositing_reason_finder,
     PaintLayer* layer,
     bool has_composited_descendants,
     bool has3d_transformed_descendants) {
@@ -190,9 +191,11 @@ static CompositingReasons SubtreeReasonsForCompositing(
     if (layer->GetLayoutObject().HasClipRelatedProperty())
       subtree_reasons |= kCompositingReasonClipsCompositingDescendants;
 
-    if (layer->GetLayoutObject().Style()->GetPosition() == EPosition::kFixed)
+    if (compositing_reason_finder.RequiresCompositingForScrollDependentPosition(
+            layer, true)) {

[flackr, 2017/04/26 15:42:36]

nit: the style, depending on where blink is at now, for annotating bools in
method calls is either:
RequiresCompositingForScrollDependentPosition(layer, true /* ignore_lcd_text */)
or
const bool ignore_lcd_text = true;
... RequiresCompositingForScrollDependentPosition(layer, ignore_lcd_text).

[smcgruer, 2017/04/26 18:05:46]

Done.

       subtree_reasons |=
-          kCompositingReasonPositionFixedWithCompositedDescendants;
+          kCompositingReasonPositionFixedOrStickyWithCompositedDescendants;
+    }
   }
 
   // A layer with preserve-3d or perspective only needs to be composited if
@@ -497,7 +500,8 @@ void CompositingRequirementsUpdater::UpdateRecursive(
     // descendant layers.
     CompositingReasons subtree_compositing_reasons =
         SubtreeReasonsForCompositing(
-            layer, child_recursion_data.subtree_is_compositing_,
+            compositing_reason_finder_, layer,
+            child_recursion_data.subtree_is_compositing_,
             any_descendant_has3d_transform);
     reasons_to_composite |= subtree_compositing_reasons;
     if (!will_be_composited_or_squashed && can_be_composited &&