Reduce PropertyTreeState construction and copies

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

Index: third_party/WebKit/Source/core/paint/ObjectPaintProperties.cpp
diff --git a/third_party/WebKit/Source/core/paint/ObjectPaintProperties.cpp b/third_party/WebKit/Source/core/paint/ObjectPaintProperties.cpp
index ae564c4d2f8bc7bcf70a5af487d9b38a298c6b25..f79de534bb3a67a83779c58444c2eda9d80e3e98 100644
--- a/third_party/WebKit/Source/core/paint/ObjectPaintProperties.cpp
+++ b/third_party/WebKit/Source/core/paint/ObjectPaintProperties.cpp
@@ -6,23 +6,25 @@
 
 namespace blink {
 
-PropertyTreeState ObjectPaintProperties::contentsProperties() const {
-  PropertyTreeState properties = *localBorderBoxProperties();
+void ObjectPaintProperties::updateContentsProperties() const {
+  DCHECK(m_localBorderBoxProperties);
+  DCHECK(!m_contentsProperties);
+
+  m_contentsProperties =
+      WTF::makeUnique<PropertyTreeState>(*m_localBorderBoxProperties);
 
   if (scrollTranslation())
-    properties.setTransform(scrollTranslation());
+    m_contentsProperties->setTransform(scrollTranslation());
 
   if (scroll())
-    properties.setScroll(scroll());
+    m_contentsProperties->setScroll(scroll());
 
   if (overflowClip())
-    properties.setClip(overflowClip());
+    m_contentsProperties->setClip(overflowClip());
   else if (cssClip())
-    properties.setClip(cssClip());
+    m_contentsProperties->setClip(cssClip());
 
   // TODO(chrishtr): cssClipFixedPosition needs to be handled somehow.
-
-  return properties;
 }
 
 }  // namespace blink