Exit VR Shell on pause (And fix a bunch of minor bugs).

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"
@@ skipping 24 matching lines @@
   web_ui()->RegisterMessageCallback(
       "doAction", base::Bind(&VrShellUIMessageHandler::HandleDoAction,
                              base::Unretained(this)));
 }
 
 void VrShellUIMessageHandler::HandleDomLoaded(const base::ListValue* args) {
   AllowJavascript();
 }
 
 void VrShellUIMessageHandler::OnJavascriptAllowed() {
-  CHECK(vr_shell_);
+  // If we don't have a VR Shell here, it means either the user manually loaded
+  // this webui page and we want to silently fail to connect to native vr shell,
+  // or VR Shell was deleted, and this webui content is also about to be
+  // deleted.
+  if (!vr_shell_)
+    return;
   vr_shell_->GetUiInterface()->SetUiCommandHandler(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);
 }