Implement a means of letting native VR Shell control the HTML UI.

chrome/browser/ui/webui/vr_shell/vr_shell_ui_message_handler.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/webui/vr_shell/vr_shell_ui_message_handler.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/values.h"
+#include "chrome/browser/android/vr_shell/ui_interface.h"
 #include "chrome/browser/android/vr_shell/ui_scene.h"
 #include "chrome/browser/android/vr_shell/vr_shell.h"
 #include "content/public/browser/web_ui.h"
 
 VrShellUIMessageHandler::VrShellUIMessageHandler() = default;
 
-VrShellUIMessageHandler::~VrShellUIMessageHandler() = default;
+VrShellUIMessageHandler::~VrShellUIMessageHandler() {
+  if (vr_shell_) {
+    vr_shell_->GetUiInterface()->SetUiMessageHandler(nullptr);
+  }
+}
 
 void VrShellUIMessageHandler::RegisterMessages() {
   vr_shell_ = vr_shell::VrShell::GetWeakPtr(web_ui()->GetWebContents());
 
   web_ui()->RegisterMessageCallback(
       "domLoaded", base::Bind(&VrShellUIMessageHandler::HandleDomLoaded,
                               base::Unretained(this)));
   web_ui()->RegisterMessageCallback(
       "updateScene", base::Bind(&VrShellUIMessageHandler::HandleUpdateScene,
                             base::Unretained(this)));
   web_ui()->RegisterMessageCallback(
       "doAction", base::Bind(&VrShellUIMessageHandler::HandleDoAction,
                              base::Unretained(this)));
 }
 
 void VrShellUIMessageHandler::HandleDomLoaded(const base::ListValue* args) {
-  if (!vr_shell_)
-    return;
+  AllowJavascript();
+}
 
+void VrShellUIMessageHandler::OnJavascriptAllowed() {
+  CHECK(vr_shell_);
+  vr_shell_->GetUiInterface()->SetUiMessageHandler(this);
   vr_shell_->OnDomContentsLoaded();
 }
 
 void VrShellUIMessageHandler::HandleUpdateScene(const base::ListValue* args) {
   if (!vr_shell_)
     return;
 
   // Copy the update instructions and handle them on the render thread.
   auto cb = base::Bind(&vr_shell::UiScene::HandleCommands,
                        base::Unretained(vr_shell_->GetScene()),
                        base::Owned(args->CreateDeepCopy().release()),
                        vr_shell::UiScene::TimeInMicroseconds());
   vr_shell_->QueueTask(cb);
 }
 
 void VrShellUIMessageHandler::HandleDoAction(const base::ListValue* args) {
   int action;
   CHECK(args->GetInteger(0, &action));
   if (vr_shell_) {
     vr_shell_->DoUiAction((vr_shell::UiAction) action);
   }
 }
+
+void VrShellUIMessageHandler::SendCommandToUi(const base::Value& value) {
+  CallJavascriptFunction("vrShellUi.command", value);
+}