Don't skip column set interval tree search for flow thread offset == 0.

third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.cpp

 /*
  * Copyright (C) 2012 Apple Inc.  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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 377 matching lines @@
             if (!previousSet)
                 break;
             columnSet = previousSet;
         }
         return columnSet;
     }
 
     ASSERT(!m_columnSetsInvalidated);
     if (m_multiColumnSetList.isEmpty())
         return nullptr;
-    if (offset <= 0)
+    if (offset < LayoutUnit())
         return m_multiColumnSetList.first();
 
     MultiColumnSetSearchAdapter adapter(offset);
     m_multiColumnSetIntervalTree.allOverlapsWithAdapter<MultiColumnSetSearchAdapter>(adapter);
 
     // If no set was found, the offset is in the flow thread overflow.
     if (!adapter.result() && !m_multiColumnSetList.isEmpty())
         return m_multiColumnSetList.last();
     return adapter.result();
 }
@@ skipping 642 matching lines @@
 {
     return MultiColumnLayoutState(m_lastSetWorkedOn);
 }
 
 void LayoutMultiColumnFlowThread::restoreMultiColumnLayoutState(const MultiColumnLayoutState& state)
 {
     m_lastSetWorkedOn = state.columnSet();
 }
 
 } // namespace blink