Global handle leak in Realm.create() fixed.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index c46df53851a5fef9e39d1b02c829d8d7073a4308..624e420f9b3cb07e2131cd93b5c3924a159d2c41 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -480,6 +480,7 @@ void Shell::RealmCreate(const v8::FunctionCallbackInfo<v8::Value>& args) {
   data->realms_ = new Persistent<Context>[++data->realm_count_];
   for (int i = 0; i < index; ++i) {
     data->realms_[i].Reset(isolate, old_realms[i]);
+    old_realms[i].Reset();
   }
   delete[] old_realms;
   Handle<ObjectTemplate> global_template = CreateGlobalTemplate(isolate);