Investigate & fix issues around usage_count and deoptimization_count

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"
 
@@ skipping 13 matching lines @@
 
   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_;
+  const Array& array_;  // Array of Code objects.
   DISALLOW_COPY_AND_ASSIGN(WeakCodeReferences);
 };
 
 }  // namespace dart
 
 #endif  // VM_WEAK_CODE_H_