Use a create-or-update pattern for faster local border box property updates

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 447 matching lines @@
     PaintPropertyTreeBuilderContext& context) {
   if (!object.needsPaintPropertyUpdate())
     return;
 
   // Avoid adding an ObjectPaintProperties for non-boxes to save memory, since
   // we don't need them at the moment.
   if (!object.isBox() && !object.hasLayer()) {
     if (auto* properties = object.getMutableForPainting().paintProperties())
       properties->clearLocalBorderBoxProperties();
   } else {
-    std::unique_ptr<ObjectPaintProperties::PropertyTreeStateWithOffset>
-        borderBoxContext =
-            wrapUnique(new ObjectPaintProperties::PropertyTreeStateWithOffset(
-                context.current.paintOffset,
-                PropertyTreeState(context.current.transform,
-                                  context.current.clip, context.currentEffect,
-                                  context.current.scroll)));
-    object.getMutableForPainting()
-        .ensurePaintProperties()
-        .setLocalBorderBoxProperties(std::move(borderBoxContext));
+    auto& properties = object.getMutableForPainting().ensurePaintProperties();
+    properties.updateLocalBorderBoxProperties(
+        context.current.paintOffset, context.current.transform,
+        context.current.clip, context.currentEffect, context.current.scroll);
   }
 }
 
 // TODO(trchen): Remove this once we bake the paint offset into frameRect.
 void PaintPropertyTreeBuilder::updateScrollbarPaintOffset(
     const LayoutObject& object,
     const PaintPropertyTreeBuilderContext& context) {
   if (!object.needsPaintPropertyUpdate())
     return;
 
@@ skipping 412 matching lines @@
 #endif
 
   updateOverflowClip(object, context);
   updatePerspective(object, context);
   updateSvgLocalToBorderBoxTransform(object, context);
   updateScrollAndScrollTranslation(object, context);
   updateOutOfFlowContext(object, context);
 }
 
 }  // namespace blink