VM: Fix race between background compiler and guarded cid update.

runtime/vm/weak_code.h

 // Copyright (c) 2014, 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_WEAK_CODE_H_
 #define VM_WEAK_CODE_H_
 
 #include "vm/allocation.h"
 #include "vm/globals.h"
 
 namespace dart {
 
 class Array;
 class Code;
 
 // Helper class to handle an array of code weak properties. Implements
 // registration and disabling of stored code objects.
 class WeakCodeReferences : public ValueObject {
  public:
   explicit WeakCodeReferences(const Array& value) : array_(value) {}
   virtual ~WeakCodeReferences() {}
 
   void Register(const Code& value);
 
   virtual void UpdateArrayTo(const Array& array) = 0;
   virtual void ReportDeoptimization(const Code& code) = 0;
   virtual void ReportSwitchingCode(const Code& code) = 0;
-  virtual void IncrementInvalidationGen() = 0;
 
   static bool IsOptimizedCode(const Array& dependent_code, const Code& code);
 
   void DisableCode();
 
   bool HasCodes() const;
 
  private:
   const Array& array_;  // Array of Code objects.
   DISALLOW_COPY_AND_ASSIGN(WeakCodeReferences);
 };
 
 }  // namespace dart
 
 #endif  // VM_WEAK_CODE_H_