Cleanup handling of NullType in type propagation.

runtime/vm/flow_graph_optimizer.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_FLOW_GRAPH_OPTIMIZER_H_
 #define VM_FLOW_GRAPH_OPTIMIZER_H_
 
 #include "vm/intermediate_language.h"
 
 namespace dart {
@@ skipping 68 matching lines @@
         parsed_function_(parsed_function),
         still_changing_(false) { }
   virtual ~FlowGraphTypePropagator() { }
 
   const ParsedFunction& parsed_function() const { return parsed_function_; }
 
   void PropagateTypes();
 
   virtual void VisitAssertAssignable(AssertAssignableComp* comp,
                                      BindInstr* instr);
-  virtual void VisitAssertBoolean(AssertBooleanComp* comp,
-                                  BindInstr* instr);
+  virtual void VisitAssertBoolean(AssertBooleanComp* comp, BindInstr* instr);
+  virtual void VisitInstanceOf(InstanceOfComp* comp, BindInstr* instr);
 
   virtual void VisitGraphEntry(GraphEntryInstr* graph_entry);
   virtual void VisitJoinEntry(JoinEntryInstr* join_entry);
   virtual void VisitBind(BindInstr* bind);
   virtual void VisitPhi(PhiInstr* phi);
   virtual void VisitParameter(ParameterInstr* param);
 
  private:
   const ParsedFunction& parsed_function_;
   bool still_changing_;
   DISALLOW_COPY_AND_ASSIGN(FlowGraphTypePropagator);
 };
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_OPTIMIZER_H_