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

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

Index: chrome/browser/ui/webui/vr_shell/vr_shell_ui_message_handler.cc
diff --git a/chrome/browser/ui/webui/vr_shell/vr_shell_ui_message_handler.cc b/chrome/browser/ui/webui/vr_shell/vr_shell_ui_message_handler.cc
index c970d84b09a05184467e30984398c8985f42c988..8975009dada602ea11cf4ef2ff7d9435504f068c 100644
--- a/chrome/browser/ui/webui/vr_shell/vr_shell_ui_message_handler.cc
+++ b/chrome/browser/ui/webui/vr_shell/vr_shell_ui_message_handler.cc
@@ -10,13 +10,18 @@
 #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());
@@ -33,9 +38,12 @@ void VrShellUIMessageHandler::RegisterMessages() {
 }
 
 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();
 }
 
@@ -58,3 +66,7 @@ void VrShellUIMessageHandler::HandleDoAction(const base::ListValue* args) {
     vr_shell_->DoUiAction((vr_shell::UiAction) action);
   }
 }
+
+void VrShellUIMessageHandler::SendCommandToUi(const base::Value& value) {
+  CallJavascriptFunction("vrShellUi.command", value);
+}