Don't invalidate rect if it's covered by fully invalidated parent's visual rect

third_party/WebKit/Source/core/paint/PaintInvalidator.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 PaintInvalidator_h
 #define PaintInvalidator_h
 
 #include "platform/geometry/LayoutRect.h"
 #include "platform/graphics/paint/GeometryMapper.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class FrameView;
 class LayoutBoxModelObject;
 class LayoutObject;
 class PaintLayer;
 struct PaintPropertyTreeBuilderContext;
 
 struct PaintInvalidatorContext {
   PaintInvalidatorContext(
       const PaintPropertyTreeBuilderContext& treeBuilderContext)
-      : treeBuilderContext(treeBuilderContext) {}
+      : treeBuilderContext(treeBuilderContext), parentContext(nullptr) {}
 
   PaintInvalidatorContext(
       const PaintPropertyTreeBuilderContext& treeBuilderContext,
       const PaintInvalidatorContext& parentContext)
       : treeBuilderContext(treeBuilderContext),
+        parentContext(&parentContext),
         forcedSubtreeInvalidationFlags(
             parentContext.forcedSubtreeInvalidationFlags),
         paintInvalidationContainer(parentContext.paintInvalidationContainer),
         paintInvalidationContainerForStackedContents(
             parentContext.paintInvalidationContainerForStackedContents),
         paintingLayer(parentContext.paintingLayer) {}
 
   // This method is temporary to adapt PaintInvalidatorContext and the legacy
   // PaintInvalidationState for code shared by old code and new code.
   virtual void mapLocalRectToPaintInvalidationBacking(const LayoutObject&,
                                                       LayoutRect&) const;
 
   const PaintPropertyTreeBuilderContext& treeBuilderContext;
+  const PaintInvalidatorContext* parentContext;
 
   enum ForcedSubtreeInvalidationFlag {
     ForcedSubtreeInvalidationChecking = 1 << 0,
     ForcedSubtreeInvalidationRectUpdate = 1 << 1,
     ForcedSubtreeFullInvalidation = 1 << 2,
     ForcedSubtreeFullInvalidationForStackedContents = 1 << 3,
     ForcedSubtreeSVGResourceChange = 1 << 4,
     // TODO(crbug.com/637313): This is temporary before we support filters in
     // paint property tree.
     ForcedSubtreeSlowPathRect = 1 << 5,
@@ skipping 55 matching lines @@
   ALWAYS_INLINE void updateContext(const LayoutObject&,
                                    PaintInvalidatorContext&);
 
   Vector<const LayoutObject*> m_pendingDelayedPaintInvalidations;
   GeometryMapper& m_geometryMapper;
 };
 
 }  // namespace blink
 
 #endif  // PaintInvalidator_h