Fix bug in optimization in the presence of externalized strings.

runtime/vm/intermediate_language.h

 // Copyright (c) 2013, 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_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 4093 matching lines @@
   virtual RawAbstractType* CompileType() const;
 
   virtual intptr_t ArgumentCount() const { return 0; }
 
   virtual bool CanDeoptimize() const { return true; }
 
   virtual bool HasSideEffect() const { return false; }
 
   virtual bool AttributesEqual(Instruction* other) const;
 
-  virtual bool AffectedBySideEffect() const { return false; }
+  virtual bool AffectedBySideEffect() const;
 
   Value* value() const { return inputs_[0]; }
 
   const ICData& unary_checks() const { return unary_checks_; }
 
   virtual Instruction* Canonicalize(FlowGraphOptimizer* optimizer);
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
  private:
@@ skipping 298 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_