Fix gradient background invalidation when HTML size changes

third_party/WebKit/Source/core/paint/BoxPaintInvalidator.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 BoxPaintInvalidator_h
 #define BoxPaintInvalidator_h
 
 #include "platform/graphics/PaintInvalidationReason.h"
 #include "wtf/Allocator.h"
 
 namespace blink {
 
 class LayoutBox;
 class LayoutRect;
 class LayoutSize;
 struct PaintInvalidatorContext;
 
 class BoxPaintInvalidator {
   STACK_ALLOCATED();
 
  public:
   BoxPaintInvalidator(const LayoutBox& box,
                       const PaintInvalidatorContext& context)
       : m_box(box), m_context(context) {}
 
   static void boxWillBeDestroyed(const LayoutBox&);
 
   PaintInvalidationReason invalidatePaintIfNeeded();
 
+  static LayoutSize previousBorderBoxSize(const LayoutBox&);
+
  private:
   bool backgroundGeometryDependsOnLayoutOverflowRect();
   bool backgroundPaintsOntoScrollingContentsLayer();
   bool shouldFullyInvalidateBackgroundOnLayoutOverflowChange(
       const LayoutRect& oldLayoutOverflow,
       const LayoutRect& newLayoutOverflow);
   void invalidateScrollingContentsBackgroundIfNeeded();
 
   PaintInvalidationReason computePaintInvalidationReason();
 
   bool incrementallyInvalidatePaint(PaintInvalidationReason,
                                     const LayoutRect& oldRect,
                                     const LayoutRect& newRect);
 
   bool needsToSavePreviousBoxGeometries();
   void savePreviousBoxGeometriesIfNeeded();
   LayoutSize previousBorderBoxSize();
   LayoutRect previousContentBoxRect();
   LayoutRect previousLayoutOverflowRect();
 
   const LayoutBox& m_box;
   const PaintInvalidatorContext& m_context;
 };
 
 }  // namespace blink
 
 #endif