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

src/debug/debug-scopes.cc

 // Copyright 2015 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/debug/debug-scopes.h"
 
 #include "src/ast/scopes.h"
 #include "src/debug/debug.h"
 #include "src/frames-inl.h"
 #include "src/globals.h"
@@ skipping 319 matching lines @@
       os << "Global:\n";
       CurrentContext()->Print(os);
       break;
 
     case ScopeIterator::ScopeTypeLocal: {
       os << "Local:\n";
       GetFunction()->shared()->scope_info()->Print();
       if (!CurrentContext().is_null()) {
         CurrentContext()->Print(os);
         if (CurrentContext()->has_extension()) {
-          Handle<Object> extension(CurrentContext()->extension(), isolate_);
+          Handle<HeapObject> extension(CurrentContext()->extension(), isolate_);
           if (extension->IsJSContextExtensionObject()) {
             extension->Print(os);
           }
         }
       }
       break;
     }
 
     case ScopeIterator::ScopeTypeWith:
       os << "With:\n";
       CurrentContext()->extension()->Print(os);
       break;
 
     case ScopeIterator::ScopeTypeCatch:
       os << "Catch:\n";
       CurrentContext()->extension()->Print(os);
       CurrentContext()->get(Context::THROWN_OBJECT_INDEX)->Print(os);
       break;
 
     case ScopeIterator::ScopeTypeClosure:
       os << "Closure:\n";
       CurrentContext()->Print(os);
       if (CurrentContext()->has_extension()) {
-        Handle<Object> extension(CurrentContext()->extension(), isolate_);
+        Handle<HeapObject> extension(CurrentContext()->extension(), isolate_);
         if (extension->IsJSContextExtensionObject()) {
           extension->Print(os);
         }
       }
       break;
 
     case ScopeIterator::ScopeTypeScript:
       os << "Script:\n";
       CurrentContext()
           ->global_object()
@@ skipping 407 matching lines @@
         isolate_, value, Object::GetPropertyOrElement(extension, key), false);
     RETURN_ON_EXCEPTION_VALUE(
         isolate_, JSObject::SetOwnPropertyIgnoreAttributes(
             scope_object, key, value, NONE), false);
   }
   return true;
 }
 
 }  // namespace internal
 }  // namespace v8