[Extensions] Don't allow built-in extensions code to be overridden
BUG=546677

Review URL: https://codereview.chromium.org/1417513003

Cr-Commit-Position: refs/heads/master@{#356654}
gin::Handle<TestServiceProvider> TestServiceProvider::Create(
    v8::Isolate* isolate) {
  return gin::CreateHandle(isolate, new TestServiceProvider());
}

gin::Handle<TestServiceProvider> TestServiceProvider::Create(
    v8::Isolate* isolate) {
  return gin::CreateHandle(isolate, new TestServiceProvider());
}
