Remove FlowThreadController and relateds.

Source/core/rendering/RenderFlowThread.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 148 matching lines @@
 
     MultiColumnSetIntervalTree m_multiColumnSetIntervalTree;
 
     bool m_regionsInvalidated : 1;
     bool m_regionsHaveUniformLogicalHeight : 1;
     bool m_pageLogicalSizeChanged : 1;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderFlowThread, isRenderFlowThread());
 
-class CurrentRenderFlowThreadMaintainer {
-    WTF_MAKE_NONCOPYABLE(CurrentRenderFlowThreadMaintainer);
-public:
-    CurrentRenderFlowThreadMaintainer(RenderFlowThread*);
-    ~CurrentRenderFlowThreadMaintainer();
-private:
-    RenderFlowThread* m_renderFlowThread;
-    RenderFlowThread* m_previousRenderFlowThread;
-};
-
 // These structures are used by PODIntervalTree for debugging.
 #ifndef NDEBUG
 template <> struct ValueToString<LayoutUnit> {
     static String string(const LayoutUnit value) { return String::number(value.toFloat()); }
 };
 
 template <> struct ValueToString<RenderMultiColumnSet*> {
     static String string(const RenderMultiColumnSet* value) { return String::format("%p", value); }
 };
 #endif
 
 } // namespace blink
 
 #endif // RenderFlowThread_h