Expose a way to make a "same-origin" realm

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 9466ab7d3a727c2fe12d70ac977df0b0cac57f35..2f6f28bb1015932c96c588e47e6d86c13a0238b3 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -548,6 +548,23 @@ void Shell::RealmCreate(const v8::FunctionCallbackInfo<v8::Value>& args) {
   args.GetReturnValue().Set(index);
 }
 
+// Realm.makeSameOrigin(i) sets the security token of i to that of the
+// current realm.
+void Shell::RealmMakeSameOrigin(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  Isolate* isolate = args.GetIsolate();
+  PerIsolateData* data = PerIsolateData::Get(isolate);
+  int index = data->RealmIndexOrThrow(args, 0);
+  if (index == -1) return;
+  if (index == 0 || index == data->realm_current_ ||
+      index == data->realm_switch_) {
+    Throw(args.GetIsolate(), "Invalid realm index");
+    return;
+  }
+
+  data->realms_[index].Get(isolate)->SetSecurityToken(
+      isolate->GetEnteredContext()->GetSecurityToken());
+}
 
 // Realm.dispose(i) disposes the reference to the realm i.
 void Shell::RealmDispose(const v8::FunctionCallbackInfo<v8::Value>& args) {
@@ -1136,6 +1153,10 @@ Local<ObjectTemplate> Shell::CreateGlobalTemplate(Isolate* isolate) {
           .ToLocalChecked(),
       FunctionTemplate::New(isolate, RealmCreate));
   realm_template->Set(
+      String::NewFromUtf8(isolate, "makeSameOrigin", NewStringType::kNormal)
+          .ToLocalChecked(),
+      FunctionTemplate::New(isolate, RealmMakeSameOrigin));
+  realm_template->Set(
       String::NewFromUtf8(isolate, "dispose", NewStringType::kNormal)
           .ToLocalChecked(),
       FunctionTemplate::New(isolate, RealmDispose));