Move code for locating the containing flow thread out of LayoutObject.

Source/core/layout/LayoutFlowThread.h

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer.
@@ skipping 38 matching lines @@
 public:
     LayoutFlowThread();
     ~LayoutFlowThread() override { }
 
     bool isLayoutFlowThread() const final { return true; }
     virtual bool isLayoutMultiColumnFlowThread() const { return false; }
     virtual bool isLayoutPagedFlowThread() const { return false; }
 
     bool supportsPaintInvalidationStateCachedOffsets() const override { return false; }
 
+    static LayoutFlowThread* locateFlowThreadContainingBlockOf(const LayoutObject&);
+
     void layout() override;
 
     // Always create a Layer for the LayoutFlowThread so that we
     // can easily avoid drawing the children directly.
     DeprecatedPaintLayerType layerTypeRequired() const final { return NormalDeprecatedPaintLayer; }
 
     // Skip past a column spanner during flow thread layout. Spanners are not laid out inside the
     // flow thread, since the flow thread is not in a spanner's containing block chain (since the
     // containing block is the multicol container).
     virtual void skipColumnSpanner(LayoutBox*, LayoutUnit logicalTopInFlowThread) { }
@@ skipping 88 matching lines @@
 };
 
 template <> struct ValueToString<LayoutMultiColumnSet*> {
     static String string(const LayoutMultiColumnSet* value) { return String::format("%p", value); }
 };
 #endif
 
 } // namespace blink
 
 #endif // LayoutFlowThread_h