Reapply r18377 it was reverted due to the unrelated bug it surfaced.

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"
 #include "vm/flow_graph.h"
 
@@ skipping 103 matching lines @@
 
   FlowGraph* flow_graph_;
 
   DISALLOW_COPY_AND_ASSIGN(FlowGraphOptimizer);
 };
 
 
 class ParsedFunction;
 
 
-class FlowGraphTypePropagator : public FlowGraphVisitor {
- public:
-  explicit FlowGraphTypePropagator(FlowGraph* flow_graph)
-      : FlowGraphVisitor(flow_graph->reverse_postorder()),
-        parsed_function_(flow_graph->parsed_function()),
-        flow_graph_(flow_graph),
-        still_changing_(false) { }
-  virtual ~FlowGraphTypePropagator() { }
-
-  const ParsedFunction& parsed_function() const { return parsed_function_; }
-
-  void PropagateTypes();
-
- private:
-  virtual void VisitBlocks();
-
-  virtual void VisitAssertAssignable(AssertAssignableInstr* instr);
-  virtual void VisitAssertBoolean(AssertBooleanInstr* instr);
-  virtual void VisitInstanceOf(InstanceOfInstr* instr);
-
-  virtual void VisitGraphEntry(GraphEntryInstr* graph_entry);
-  virtual void VisitJoinEntry(JoinEntryInstr* join_entry);
-  virtual void VisitPhi(PhiInstr* phi);
-  virtual void VisitParameter(ParameterInstr* param);
-  virtual void VisitPushArgument(PushArgumentInstr* bind);
-
-  const ParsedFunction& parsed_function_;
-  FlowGraph* flow_graph_;
-  bool still_changing_;
-  DISALLOW_COPY_AND_ASSIGN(FlowGraphTypePropagator);
-};
-
-
 // Loop invariant code motion.
 class LICM : public AllStatic {
  public:
   static void Optimize(FlowGraph* flow_graph);
 
  private:
   static void Hoist(ForwardInstructionIterator* it,
                     BlockEntryInstr* pre_header,
                     Instruction* current);
 
@@ skipping 76 matching lines @@
 
   // Worklists of blocks and definitions.
   GrowableArray<BlockEntryInstr*> block_worklist_;
   GrowableArray<Definition*> definition_worklist_;
 };
 
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_OPTIMIZER_H_