VM: Remove unnecesary load of isolate in some stubs.

runtime/vm/isolate.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_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/atomic.h"
@@ skipping 203 matching lines @@
   uint64_t pause_capability() const { return pause_capability_; }
   void set_terminate_capability(uint64_t value) {
     terminate_capability_ = value;
   }
   uint64_t terminate_capability() const { return terminate_capability_; }
 
   void SendInternalLibMessage(LibMsgId msg_id, uint64_t capability);
 
   Heap* heap() const { return heap_; }
   void set_heap(Heap* value) { heap_ = value; }
-  static intptr_t heap_offset() { return OFFSET_OF(Isolate, heap_); }
 
   ObjectStore* object_store() const { return object_store_; }
   void set_object_store(ObjectStore* value) { object_store_ = value; }
 
   ApiState* api_state() const { return api_state_; }
   void set_api_state(ApiState* value) { api_state_ = value; }
 
   void set_init_callback_data(void* value) {
     init_callback_data_ = value;
   }
@@ skipping 789 matching lines @@
   intptr_t* spawn_count_;
 
   Dart_IsolateFlags isolate_flags_;
   bool paused_;
   bool errors_are_fatal_;
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_