[Extensions] Expand bindings access checks

BUG=601149
BUG=601073

Review URL: https://codereview.chromium.org/1866103002

Cr-Commit-Position: refs/heads/master@{#387710}
void RuntimeCustomBindings::GetManifest(
    const v8::FunctionCallbackInfo<v8::Value>& args) {
  CHECK(context()->extension());

  scoped_ptr<V8ValueConverter> converter(V8ValueConverter::create());
  args.GetReturnValue().Set(converter->ToV8Value(
      context()->extension()->manifest()->value(), context()->v8_context()));
}

void RuntimeCustomBindings::GetManifest(
    const v8::FunctionCallbackInfo<v8::Value>& args) {
  CHECK(context()->extension());

  scoped_ptr<V8ValueConverter> converter(V8ValueConverter::create());
  args.GetReturnValue().Set(converter->ToV8Value(
      context()->extension()->manifest()->value(), context()->v8_context()));
}
