Break out WeakCodeReferences to own file in preparation to use it outside object.cc.

runtime/vm/weak_code.h

Index: runtime/vm/weak_code.h
===================================================================
--- runtime/vm/weak_code.h	(revision 0)
+++ runtime/vm/weak_code.h	(revision 0)
@@ -0,0 +1,40 @@
+// 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;
+
+  static bool IsOptimizedCode(const Array& dependent_code, const Code& code);
+
+  void DisableCode();
+
+ private:
+  const Array& array_;
+  DISALLOW_COPY_AND_ASSIGN(WeakCodeReferences);
+};
+
+}  // namespace dart
+
+#endif  // VM_WEAK_CODE_H_