Switch the Root Layer Scrolls codepath to use root clip paint properties

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintPropertyTreeBuilder.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutInline.h"
@@ skipping 32 matching lines @@
     {
         DEFINE_STATIC_REF(ScrollPaintPropertyNode, rootScroll, (ScrollPaintPropertyNode::create(nullptr, rootTransformNode(), IntSize(), IntSize(), false, false)));
         return rootScroll;
     }
 }
 
 PaintPropertyTreeBuilderContext PaintPropertyTreeBuilder::setupInitialContext()
 {
     PaintPropertyTreeBuilderContext context;
 
-    // TODO(pdr): Update the root layer scrolling paths to use the static root nodes.
+    context.current.clip = context.absolutePosition.clip = context.fixedPosition.clip = rootClipNode();
+
+    // TODO(pdr): Update the root layer scrolling paths to use the static root nodes for transform, effect, and scroll.
     if (RuntimeEnabledFeatures::rootLayerScrollingEnabled())
         return context;
 
     context.current.transform = context.absolutePosition.transform = context.fixedPosition.transform = rootTransformNode();
     context.current.scroll = context.absolutePosition.scroll = context.fixedPosition.scroll = rootScrollNode();
-    context.current.clip = context.absolutePosition.clip = context.fixedPosition.clip = rootClipNode();
     context.currentEffect = rootEffectNode();
 
     // Ensure scroll tree properties are reset. They will be rebuilt during the tree walk.
     rootScrollNode()->clearMainThreadScrollingReasons();
 
     return context;
 }
 
 void createOrUpdateFrameViewPreTranslation(FrameView& frameView,
     PassRefPtr<const TransformPaintPropertyNode> parent,
@@ skipping 249 matching lines @@
     // Avoid adding an ObjectPaintProperties for non-boxes to save memory, since we don't need them at the moment.
     if (!object.isBox() && !object.hasLayer())
         return;
 
     std::unique_ptr<ObjectPaintProperties::LocalBorderBoxProperties> borderBoxContext =
         wrapUnique(new ObjectPaintProperties::LocalBorderBoxProperties);
     borderBoxContext->paintOffset = context.current.paintOffset;
     borderBoxContext->geometryPropertyTreeState = GeometryPropertyTreeState(context.current.transform, context.current.clip, context.currentEffect);
     borderBoxContext->scroll = context.current.scroll;
 
-    if (!context.current.clip) {
-        DCHECK(object.isLayoutView());
-        DCHECK(toLayoutView(object).frameView()->frame().isMainFrame());
-        DCHECK(RuntimeEnabledFeatures::rootLayerScrollingEnabled());
-        borderBoxContext->geometryPropertyTreeState.clip = ClipPaintPropertyNode::create(nullptr, context.current.transform, FloatRoundedRect(LayoutRect::infiniteIntRect()));
-        context.current.clip = borderBoxContext->geometryPropertyTreeState.clip.get();
-    }
-
     object.getMutableForPainting().ensureObjectPaintProperties().setLocalBorderBoxProperties(std::move(borderBoxContext));
 
 }
 
 // TODO(trchen): Remove this once we bake the paint offset into frameRect.
 void PaintPropertyTreeBuilder::updateScrollbarPaintOffset(const LayoutObject& object, const PaintPropertyTreeBuilderContext& context)
 {
     IntPoint roundedPaintOffset = roundedIntPoint(context.current.paintOffset);
     if (roundedPaintOffset != IntPoint() && object.isBoxModelObject()) {
         if (PaintLayerScrollableArea* scrollableArea = toLayoutBoxModelObject(object).getScrollableArea()) {
@@ skipping 250 matching lines @@
         return;
 
     updateOverflowClip(object, context);
     updatePerspective(object, context);
     updateSvgLocalToBorderBoxTransform(object, context);
     updateScrollAndScrollTranslation(object, context);
     updateOutOfFlowContext(object, context);
 }
 
 } // namespace blink