Store previous painting clip rects on FragmentData.

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

 // Copyright 2017 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.
 
 #ifndef FragmentData_h
 #define FragmentData_h
 
 #include "core/paint/ObjectPaintProperties.h"
 
 namespace blink {
 
 class ObjectPaintProperties;
 
 // Represents the data for a particular fragment of a LayoutObject.
 // Only LayoutObjects with a self-painting PaintLayer may have more than one
 // FragmentDeta, and even then only when they are inside of multicol.
 // See README.md.
 class CORE_EXPORT FragmentData {
  public:
   static std::unique_ptr<FragmentData> Create() {
     return WTF::WrapUnique(new FragmentData());
   }
 
   ObjectPaintProperties* PaintProperties() const {
     return paint_properties_.get();
   }
   ObjectPaintProperties& EnsurePaintProperties();
   void ClearPaintProperties();
 
+  ClipRects* PreviousPaintingClipRects() const {

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

Are there other clip rects we expect to store in FragmentData that aren't
painting related? If not we could remove Painting from names.

I see we already have similar named member data and methods in PaintLayer, but I
have same question there. It's a PaintLayer, so I would implicitly default to
assuming clip rects stored or interacted with there are painting related. Do we
need painting in the names?

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

Done.

+    DCHECK(RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled());
+    return previous_painting_clip_rects_.Get();
+  }
+  void SetPreviousPaintingClipRects(ClipRects& clip_rects) {
+    previous_painting_clip_rects_ = &clip_rects;
+  }
+  void ClearPreviousPaintingClipRects() {
+    previous_painting_clip_rects_.Clear();
+  }
+
   FragmentData* NextFragment() { return next_fragment_.get(); }
 
  private:
   // Holds references to the paint property nodes created by this object.
   std::unique_ptr<ObjectPaintProperties> paint_properties_;
 
+  // These are used to detect changes to clipping that might invalidate
+  // subsequence caching or paint phase optimizations.
+  RefPtr<ClipRects> previous_painting_clip_rects_;
+
   std::unique_ptr<FragmentData> next_fragment_;
 };
 
 }  // namespace blink
 
 #endif  // FragmentData_h