[New Multicolumn] Don't return the wrong flow thread from locateFlowThreadContainingBlock().

Source/core/layout/LayoutState.h

Index: Source/core/layout/LayoutState.h
diff --git a/Source/core/layout/LayoutState.h b/Source/core/layout/LayoutState.h
index 06527f70480c1a48b621f4255b9138840610a495..a227950f45f7f8c4ce407952fae60982de8cdaa7 100644
--- a/Source/core/layout/LayoutState.h
+++ b/Source/core/layout/LayoutState.h
@@ -75,6 +75,9 @@ public:
 
     LayoutFlowThread* flowThread() const { return m_flowThread; }
 
+    // Used to temporarily set m_flowThread to nullptr. Needed because of crbug.com/370461 (list item markers).
+    void setFlowThread(LayoutFlowThread* flowThread) { m_flowThread = flowThread; }
+
     ColumnInfo* columnInfo() const { return m_columnInfo; }
 
     LayoutObject& layoutObject() const { return m_renderer; }