Shifting layer position for sticky element to avoid passing unnessary variable to cc

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

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index abd711d097e33fed7cec2f2ad8f59fe7989654c9..8145c245f57b981b1ec2c07fb505ccf56d4f1e28 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -281,22 +281,20 @@ void CompositedLayerMapping::UpdateBackdropFilters(const ComputedStyle& style) {
       OwningLayer().CreateCompositorFilterOperationsForBackdropFilter(style));
 }
 
+bool CompositedLayerMapping::UsesCompositedStickyPosition() const {
+  return GetLayoutObject().Style()->GetPosition() == EPosition::kSticky &&
+         (owning_layer_.AncestorOverflowLayer()->IsRootLayer()
+              ? GetLayoutObject().View()->GetFrameView()->IsScrollable()
+              : owning_layer_.AncestorOverflowLayer()
+                    ->NeedsCompositedScrolling());
+}
+
 void CompositedLayerMapping::UpdateStickyConstraints(
     const ComputedStyle& style) {
-  bool sticky = style.GetPosition() == EPosition::kSticky;
   const PaintLayer* ancestor_overflow_layer =
       owning_layer_.AncestorOverflowLayer();
-  // TODO(flackr): Do we still need this?
-  if (sticky) {
-    if (!ancestor_overflow_layer->IsRootLayer()) {
-      sticky = ancestor_overflow_layer->NeedsCompositedScrolling();
-    } else {
-      sticky = GetLayoutObject().View()->GetFrameView()->IsScrollable();
-    }
-  }
-
   WebLayerStickyPositionConstraint web_constraint;
-  if (sticky) {
+  if (UsesCompositedStickyPosition()) {
     const StickyConstraintsMap& constraints_map =
         ancestor_overflow_layer->GetScrollableArea()->GetStickyConstraintsMap();
     const StickyPositionScrollingConstraints& constraints =
@@ -1128,16 +1126,11 @@ void CompositedLayerMapping::UpdateMainGraphicsLayerGeometry(
     const IntRect& relative_compositing_bounds,
     const IntRect& local_compositing_bounds,
     const IntPoint& graphics_layer_parent_location) {
-  graphics_layer_->SetPosition(FloatPoint(
-      relative_compositing_bounds.Location() - graphics_layer_parent_location));
-  graphics_layer_->SetOffsetFromLayoutObject(
-      ToIntSize(local_compositing_bounds.Location()));
-  // Find the layout offset of the unshifted sticky box within its parent
-  // composited layer. This information is used by the compositor side to
-  // compute the additional offset required to keep the element stuck under
-  // compositor scrolling.
-  FloatSize main_thread_sticky_offset;
-  if (GetLayoutObject().Style()->GetPosition() == EPosition::kSticky) {
+  // Find and remove the offset applied for sticky position if the compositor
+  // will shift the layer for sticky position to avoid offsetting the layer
+  // twice.
+  FloatSize offset_for_sticky_position;
+  if (UsesCompositedStickyPosition()) {
     const StickyConstraintsMap& constraints_map =
         owning_layer_.AncestorOverflowLayer()
             ->GetScrollableArea()
@@ -1145,11 +1138,15 @@ void CompositedLayerMapping::UpdateMainGraphicsLayerGeometry(
     const StickyPositionScrollingConstraints& constraints =
         constraints_map.at(&owning_layer_);
 
-    main_thread_sticky_offset =
+    offset_for_sticky_position =
         constraints.GetOffsetForStickyPosition(constraints_map);
   }
-  graphics_layer_->SetOffsetForStickyPosition(
-      RoundedIntSize(main_thread_sticky_offset));
+  graphics_layer_->SetPosition(
+      FloatPoint(relative_compositing_bounds.Location() -
+                 graphics_layer_parent_location) -
+      offset_for_sticky_position);
+  graphics_layer_->SetOffsetFromLayoutObject(
+      ToIntSize(local_compositing_bounds.Location()));
 
   FloatSize old_size = graphics_layer_->Size();
   const FloatSize contents_size(relative_compositing_bounds.Size());