Use 16 instead of 4 for determining member offsets.

src/heap/heap-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_HEAP_INL_H_
 #define V8_HEAP_HEAP_INL_H_
 
 #include <cmath>
 
 #include "src/base/platform/platform.h"
@@ skipping 569 matching lines @@
                           const v8::GCCallbackFlags callbackFlags) {
   const char* collector_reason = NULL;
   GarbageCollector collector = SelectGarbageCollector(space, &collector_reason);
   return CollectGarbage(collector, gc_reason, collector_reason, callbackFlags);
 }
 
 
 Isolate* Heap::isolate() {
   return reinterpret_cast<Isolate*>(
       reinterpret_cast<intptr_t>(this) -
-      reinterpret_cast<size_t>(reinterpret_cast<Isolate*>(4)->heap()) + 4);
+      reinterpret_cast<size_t>(reinterpret_cast<Isolate*>(16)->heap()) + 16);
 }
 
 
 // Calls the FUNCTION_CALL function and retries it up to three times
 // to guarantee that any allocations performed during the call will
 // succeed if there's enough memory.
 
 // Warning: Do not use the identifiers __object__, __maybe_object__ or
 // __scope__ in a call to this macro.
 
@@ skipping 168 matching lines @@
 
 void VerifySmisVisitor::VisitPointers(Object** start, Object** end) {
   for (Object** current = start; current < end; current++) {
     CHECK((*current)->IsSmi());
   }
 }
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_HEAP_INL_H_