Avoid stretching the parent of a column spanner.

Source/core/layout/LayoutPagedFlowThread.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 LayoutPagedFlowThread_h
 #define LayoutPagedFlowThread_h
 
 #include "core/layout/LayoutMultiColumnFlowThread.h"
 
 namespace blink {
 
 // A flow thread for paged overflow. FIXME: The current implementation relies on the multicol
 // implementation, but it in the long run it would be better to have what's common between
 // LayoutMultiColumnFlowThread and LayoutPagedFlowThread in LayoutFlowThread, and have both of them
 // inherit from that one.
 class LayoutPagedFlowThread : public LayoutMultiColumnFlowThread {
 public:
     static LayoutPagedFlowThread* createAnonymous(Document&, const ComputedStyle& parentStyle);
 
     LayoutBlockFlow* pagedBlockFlow() const { return toLayoutBlockFlow(parent()); }
 
+    // Return the number of pages. Will never be less than 1.
+    int pageCount();
+
     virtual bool isLayoutPagedFlowThread() const override { return true; }
     virtual const char* name() const override { return "LayoutPagedFlowThread"; }
     virtual bool needsNewWidth() const override;
     virtual void updateLogicalWidth() override;
     virtual void layout();
 
 private:
     virtual bool descendantIsValidColumnSpanner(LayoutObject* /*descendant*/) const override { return false; }
 };
 
 } // namespace blink
 
 #endif // LayoutPagedFlowThread_h