Revert r23330 and r23136 because of a bug with loop invariant code motion.

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 184 matching lines @@
 // Loop invariant code motion.
 class LICM : public ValueObject {
  public:
   explicit LICM(FlowGraph* flow_graph);
 
   void Optimize();
 
  private:
   FlowGraph* flow_graph() const { return flow_graph_; }
 
-  bool MayHoist(Instruction* instr, BlockEntryInstr* pre_header);
-
   void Hoist(ForwardInstructionIterator* it,
              BlockEntryInstr* pre_header,
              Instruction* current);
 
   void TryHoistCheckSmiThroughPhi(ForwardInstructionIterator* it,
                                   BlockEntryInstr* header,
                                   BlockEntryInstr* pre_header,
                                   CheckSmiInstr* current);
 
   FlowGraph* const flow_graph_;
@@ skipping 148 matching lines @@
 // Optimize spill stores inside try-blocks by identifying values that always
 // contain a single known constant at catch block entry.
 class TryCatchAnalyzer : public AllStatic {
  public:
   static void Optimize(FlowGraph* flow_graph);
 };
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_OPTIMIZER_H_