Store previous painting clip rects on FragmentData.

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 <memory>
 #include "core/dom/DOMNodeIds.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
@@ skipping 1173 matching lines @@
 
 void PaintPropertyTreeBuilder::UpdatePaintProperties(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& full_context) {
   bool needs_paint_properties =
       NeedsPaintOffsetTranslation(object) || NeedsTransform(object) ||
       NeedsEffect(object) || NeedsTransformForNonRootSVG(object) ||
       NeedsFilter(object) || NeedsCssClip(object) ||
       NeedsScrollbarPaintOffset(object) || NeedsOverflowScroll(object) ||
       NeedsPerspective(object) || NeedsSVGLocalToBorderBoxTransform(object) ||
-      NeedsScrollTranslation(object) || NeedsCssClipFixedPosition(object);
+      NeedsScrollTranslation(object) ||
+      NeedsCssClipFixedPosition(object)
+      // These are neeed because we store previous painting clip rects on

[wkorman, 2017/05/01 20:29:24]

neeed -> needed

+      // ObjectPaintProperties.

[wkorman, 2017/05/01 20:29:24]

Comment looks stale -- we're storing them in FragmentData now.

+      ||
+      (object.HasLayer() &&
+       ToLayoutBoxModelObject(object).Layer()->SupportsSubsequenceCaching()) ||

[wkorman, 2017/05/01 20:29:24]

How does subsequence caching support on a layer mean it needs paint properties?
The below re: clip related properties seems answered by the comment above but
it's not immediately apparent to me how that relates to subsequence caching.

It looks like this logic is essentially taken from here:

https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/paint/Pre...

and the comment there provides more detail, so maybe just copying it over here
as well.

[chrishtr, 2017/05/01 21:43:54]

I no longer need this code actually, now that the data is stored on
FragmentData.

+      object.HasClipRelatedProperty();
 
   bool had_paint_properties = object.PaintProperties();
 
   if (needs_paint_properties) {
     object.GetMutableForPainting().EnsurePaintProperties();
   } else {
     object.GetMutableForPainting().ClearPaintProperties();
     if (had_paint_properties)
       full_context.force_subtree_update = true;
   }
@@ skipping 65 matching lines @@
                            context.force_subtree_update);
 
     context.force_subtree_update |= object.SubtreeNeedsPaintPropertyUpdate();
   }
 
   if (object.CanContainAbsolutePositionObjects())
     context.container_for_absolute_position = &object;
 }
 
 }  // namespace blink