Fix bug in double unboxing.

runtime/vm/object.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_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 2101 matching lines @@
                        bool is_const,
                        const Class& owner,
                        intptr_t token_pos);
 
   // Allocate new field object, clone values from this field. The
   // owner of the clone is new_owner.
   RawField* Clone(const Class& new_owner) const;
 
   static intptr_t value_offset() { return OFFSET_OF(RawField, value_); }
 
+  static intptr_t kind_bits_offset() { return OFFSET_OF(RawField, kind_bits_); }
+
   intptr_t token_pos() const { return raw_ptr()->token_pos_; }
 
   bool has_initializer() const {
     return HasInitializerBit::decode(raw_ptr()->kind_bits_);
   }
   void set_has_initializer(bool has_initializer) const {
     set_kind_bits(HasInitializerBit::update(has_initializer,
                                             raw_ptr()->kind_bits_));
   }
 
@@ skipping 94 matching lines @@
   static bool IsGetterName(const String& function_name);
   static bool IsSetterName(const String& function_name);
 
   // When we print a field to a JSON stream, we want to make it appear
   // that the value is a property of the field, so we allow the actual
   // instance to be supplied here.
   virtual void PrintToJSONStreamWithInstance(
       JSONStream* stream, const Instance& instance, bool ref) const;
 
  private:
+  friend class StoreInstanceFieldInstr;  // Generated code access to bit field.
+
   enum {
-    kConstBit = 1,
+    kConstBit = 0,
     kStaticBit,
     kFinalBit,
     kHasInitializerBit,
     kUnboxingCandidateBit
   };
   class ConstBit : public BitField<bool, kConstBit, 1> {};
   class StaticBit : public BitField<bool, kStaticBit, 1> {};
   class FinalBit : public BitField<bool, kFinalBit, 1> {};
   class HasInitializerBit : public BitField<bool, kHasInitializerBit, 1> {};
   class UnboxingCandidateBit : public BitField<bool,
@@ skipping 4311 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_