[runtime] Use "the hole" instead of smi 0 as sentinel for context extension.

src/factory.cc

 // Copyright 2014 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.
 
 #include "src/factory.h"
 
 #include "src/allocation-site-scopes.h"
 #include "src/base/bits.h"
 #include "src/bootstrapper.h"
 #include "src/conversions.h"
@@ skipping 746 matching lines @@
   return context_table;
 }
 
 
 Handle<Context> Factory::NewModuleContext(Handle<ScopeInfo> scope_info) {
   Handle<FixedArray> array =
       NewFixedArray(scope_info->ContextLength(), TENURED);
   array->set_map_no_write_barrier(*module_context_map());
   // Instance link will be set later.
   Handle<Context> context = Handle<Context>::cast(array);
-  context->set_extension(Smi::FromInt(0));
+  context->set_extension(*the_hole_value());
   return context;
 }
 
 
 Handle<Context> Factory::NewFunctionContext(int length,
                                             Handle<JSFunction> function) {
   DCHECK(length >= Context::MIN_CONTEXT_SLOTS);
   Handle<FixedArray> array = NewFixedArray(length);
   array->set_map_no_write_barrier(*function_context_map());
   Handle<Context> context = Handle<Context>::cast(array);
   context->set_closure(*function);
   context->set_previous(function->context());
-  context->set_extension(Smi::FromInt(0));
+  context->set_extension(*the_hole_value());
   context->set_native_context(function->native_context());
   return context;
 }
 
 
 Handle<Context> Factory::NewCatchContext(Handle<JSFunction> function,
                                          Handle<Context> previous,
                                          Handle<String> name,
                                          Handle<Object> thrown_object) {
   STATIC_ASSERT(Context::MIN_CONTEXT_SLOTS == Context::THROWN_OBJECT_INDEX);
@@ skipping 1542 matching lines @@
 }
 
 
 Handle<Object> Factory::ToBoolean(bool value) {
   return value ? true_value() : false_value();
 }
 
 
 }  // namespace internal
 }  // namespace v8