Implement incremental paint property tree rebuilding

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

Index: third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
diff --git a/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h b/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
index 24a60a96f90161c15e7736ec7149f7d90b846124..07eea523491c895dbdd002b50ecbd6f8ee7fe31d 100644
--- a/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
+++ b/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
@@ -143,6 +143,7 @@ class CORE_EXPORT ObjectPaintProperties {
   void clearCssClipFixedPosition() { m_cssClipFixedPosition = nullptr; }
   void clearInnerBorderRadiusClip() { m_innerBorderRadiusClip = nullptr; }
   void clearOverflowClip() { m_overflowClip = nullptr; }
+  void clearLocalBorderBoxProperties() { m_localBorderBoxProperties = nullptr; }
   void clearPerspective() { m_perspective = nullptr; }
   void clearSvgLocalToBorderBoxTransform() {
     m_svgLocalToBorderBoxTransform = nullptr;
@@ -209,6 +210,45 @@ class CORE_EXPORT ObjectPaintProperties {
     return updateProperty(m_overflowClip, std::forward<Args>(args)...);
   }
 
+  std::unique_ptr<ObjectPaintProperties> clone() const {

[chrishtr, 2016/10/21 22:03:09]

It would be cool to make this with copy constructors to make it future-proof to
added objects. But
I think that might not be possible because you'd have to subclass RefPtr or
something.

[pdr., 2016/10/26 03:10:48]

I played with this for a while but couldn't find a clean implementation using
copy constructors :/ They are not allowed on RefCounted objects, and using a
copy constructor for ObjectPaintProperties ended up being more confusing because
it works differently than the regular properties.

I have put all clone functions (ObjectPaintProperties, and {Transform, Effect,
etc..}PaintPropertyNode) behind debug checks and added comments describing what
they do.

+    std::unique_ptr<ObjectPaintProperties> cloned = create();
+    if (m_paintOffsetTranslation)
+      cloned->m_paintOffsetTranslation = m_paintOffsetTranslation->clone();
+    if (m_transform)
+      cloned->m_transform = m_transform->clone();
+    if (m_effect)
+      cloned->m_effect = m_effect->clone();
+    if (m_cssClip)
+      cloned->m_cssClip = m_cssClip->clone();
+    if (m_cssClipFixedPosition)
+      cloned->m_cssClipFixedPosition = m_cssClipFixedPosition->clone();
+    if (m_innerBorderRadiusClip)
+      cloned->m_innerBorderRadiusClip = m_innerBorderRadiusClip->clone();
+    if (m_overflowClip)
+      cloned->m_overflowClip = m_overflowClip->clone();
+    if (m_perspective)
+      cloned->m_perspective = m_perspective->clone();
+    if (m_svgLocalToBorderBoxTransform) {
+      cloned->m_svgLocalToBorderBoxTransform =
+          m_svgLocalToBorderBoxTransform->clone();
+    }
+    if (m_scrollTranslation)
+      cloned->m_scrollTranslation = m_scrollTranslation->clone();
+    if (m_scrollbarPaintOffset)
+      cloned->m_scrollbarPaintOffset = m_scrollbarPaintOffset->clone();
+    if (m_scroll)
+      cloned->m_scroll = m_scroll->clone();
+    if (m_localBorderBoxProperties) {
+      auto& state = m_localBorderBoxProperties->propertyTreeState;
+      cloned->m_localBorderBoxProperties =
+          wrapUnique(new PropertyTreeStateWithOffset(
+              m_localBorderBoxProperties->paintOffset,
+              PropertyTreeState(state.transform(), state.clip(), state.effect(),
+                                state.scroll())));
+    }
+    return cloned;
+  }
+
  private:
   ObjectPaintProperties() {}