Only store previous clip rects for PaintLayers that support subsequences.

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

 // 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.
 
 #ifndef PrePaintTreeWalk_h
 #define PrePaintTreeWalk_h
 
 #include "core/paint/ClipRect.h"
 #include "core/paint/PaintInvalidator.h"
 #include "core/paint/PaintPropertyTreeBuilder.h"
 
 namespace blink {
 
 class FrameView;
 class LayoutObject;
 class PropertyTreeState;
 struct PrePaintTreeWalkContext;
 
 // This class walks the whole layout tree, beginning from the root FrameView,
 // across frame boundaries. Helper classes are called for each tree node to
 // perform actual actions.  It expects to be invoked in InPrePaint phase.
-class PrePaintTreeWalk {
+class CORE_EXPORT PrePaintTreeWalk {

[pdr., 2017/04/12 18:40:06]

Is this only needed for tests?

[chrishtr, 2017/04/13 02:05:59]

Yes.

  public:
   PrePaintTreeWalk() {}
   void Walk(FrameView& root_frame);
 
  private:
   void Walk(FrameView&, const PrePaintTreeWalkContext&);
   void Walk(const LayoutObject&, const PrePaintTreeWalkContext&);
 
+  bool ShouldEarlyOut(const LayoutObject&,
+                      const PrePaintTreeWalkContext& parent_context,
+                      bool& needs_tree_builder_context_update);
+
   // Invalidates paint-layer painting optimizations, such as subsequence caching
   // and empty paint phase optimizations if clips from the context have changed.
   ALWAYS_INLINE void InvalidatePaintLayerOptimizationsIfNeeded(
       const LayoutObject&,
       PrePaintTreeWalkContext&);
 
   // Returns in |clipRect| the clip applied to children for the given
   // contaiing block context + effect, in the space of ancestorState adjusted
   // by ancestorPaintOffset.
   ALWAYS_INLINE void ComputeClipRectForContext(
@@ skipping 10 matching lines @@
   NeedsTreeBuilderContextUpdate(const LayoutObject&,
                                 const PrePaintTreeWalkContext&);
 
   PaintPropertyTreeBuilder property_tree_builder_;
   PaintInvalidator paint_invalidator_;
 };
 
 }  // namespace blink
 
 #endif  // PrePaintTreeWalk_h