Implement incremental paint property tree rebuilding

third_party/WebKit/Source/platform/graphics/paint/ScrollPaintPropertyNode.h

 // Copyright 2016 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 ScrollPaintPropertyNode_h
 #define ScrollPaintPropertyNode_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatSize.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
@@ skipping 73 matching lines @@
     return m_mainThreadScrollingReasons;
   }
   bool hasMainThreadScrollingReasons(MainThreadScrollingReasons reasons) const {
     return m_mainThreadScrollingReasons & reasons;
   }
   void addMainThreadScrollingReasons(MainThreadScrollingReasons reasons) {
     m_mainThreadScrollingReasons |= reasons;
   }
   void clearMainThreadScrollingReasons() { m_mainThreadScrollingReasons = 0; }
 
+#if DCHECK_IS_ON()
+  // The clone function is used by FindPropertiesNeedingUpdate.h for recording
+  // a scroll node before it has been updated, to later detect changes.
+  PassRefPtr<ScrollPaintPropertyNode> clone() const {
+    RefPtr<ScrollPaintPropertyNode> cloned =
+        adoptRef(new ScrollPaintPropertyNode(
+            m_parent, m_scrollOffsetTranslation, m_clip, m_bounds,
+            m_userScrollableHorizontal, m_userScrollableVertical));
+    cloned->addMainThreadScrollingReasons(m_mainThreadScrollingReasons);
+    return cloned;
+  }
+
+  // The equality operator is used by FindPropertiesNeedingUpdate.h for checking
+  // if a scroll node has changed.
+  bool operator==(const ScrollPaintPropertyNode& o) const {
+    // TODO(pdr): Check main thread scrolling reason equality as well. We do
+    // not yet mark nodes as needing a paint property update on main thread
+    // scrolling reason changes. See: See: https://crbug.com/664672.
+    return m_parent == o.m_parent &&
+           m_scrollOffsetTranslation == o.m_scrollOffsetTranslation &&
+           m_clip == o.m_clip && m_bounds == o.m_bounds &&
+           m_userScrollableHorizontal == o.m_userScrollableHorizontal &&
+           m_userScrollableVertical == o.m_userScrollableVertical;
+  }
+#endif
+
  private:
   ScrollPaintPropertyNode(
       PassRefPtr<ScrollPaintPropertyNode> parent,
       PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
       IntSize clip,
       IntSize bounds,
       bool userScrollableHorizontal,
       bool userScrollableVertical)
       : m_parent(parent),
         m_scrollOffsetTranslation(scrollOffsetTranslation),
@@ skipping 17 matching lines @@
   // TODO(pdr): Add a bit for whether this is affected by page scale.
 };
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const ScrollPaintPropertyNode&, std::ostream*);
 
 }  // namespace blink
 
 #endif  // ScrollPaintPropertyNode_h