Add missing method on RuntimeHolder. (#3742)

content_handler/runtime_holder.cc

@@ -254,6 +254,10 @@ std::string RuntimeHolder::GetUIIsolateName() {
   return runtime_->GetIsolateName();
 }
 
+std::string RuntimeHolder::DefaultRouteName() {
+  return "/";
+}
+
 void RuntimeHolder::ScheduleFrame() {
   if (pending_invalidation_ || deferred_invalidation_callback_)
     return;

content_handler/runtime_holder.h

@@ -51,6 +51,7 @@ class RuntimeHolder : public blink::RuntimeDelegate,
 
  private:
   // |blink::RuntimeDelegate| implementation:
+  std::string DefaultRouteName() override;
   void ScheduleFrame() override;
   void Render(std::unique_ptr<flow::LayerTree> layer_tree) override;
   void UpdateSemantics(std::vector<blink::SemanticsNode> update) override;