[New Multicolumn] Let a spanner's containing block be the multicol container.

Source/core/rendering/RenderMultiColumnSpannerSet.h

-// Copyright 2014 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 RenderMultiColumnSpannerSet_h
-#define RenderMultiColumnSpannerSet_h
-
-#include "core/rendering/RenderMultiColumnSet.h"
-
-namespace blink {
-
-// "Column" set for column-span:all elements. Positions the portion of the flow thread that a
-// spanner takes up. The actual renderer that sets column-span all is laid out as part of flow
-// thread layout (although it cannot use the flow thread width when calculating its own with; it has
-// to pretend that the containing block is the multicol container, not the flow
-// thread). RenderMultiColumnSpannerSet just makes sure that it's positioned correctly among other
-// column sets, within the multicol container.
-//
-// FIXME: should consider not inheriting from RenderMultiColumnSet (but rather from some common base
-// class). Most of what's in RenderMultiColumnSet is of no interest to us.
-class RenderMultiColumnSpannerSet final : public RenderMultiColumnSet {
-public:
-    virtual bool isOfType(RenderObjectType type) const override { return type == RenderObjectRenderMultiColumnSpannerSet || RenderMultiColumnSet::isOfType(type); }
-
-    static RenderMultiColumnSpannerSet* createAnonymous(RenderMultiColumnFlowThread*, RenderStyle* parentStyle, RenderBox*);
-
-    RenderBox* rendererInFlowThread() const { return m_rendererInFlowThread; }
-
-protected:
-    virtual bool recalculateColumnHeight(BalancedHeightCalculation) override;
-    virtual const char* renderName() const override;
-
-private:
-    RenderMultiColumnSpannerSet(RenderMultiColumnFlowThread*, RenderBox*);
-
-    RenderBox* m_rendererInFlowThread; // The actual column-span:all renderer inside the flow thread.
-};
-
-DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderMultiColumnSpannerSet, isRenderMultiColumnSpannerSet());
-
-} // namespace blink
-
-#endif