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

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 0f8a6325821e161b084a3cb9df87059be753d00a..7eb33f110f6836998ec784e8f325605d9862e22a 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
@@ -42,7 +42,12 @@ void VrShellUIMessageHandler::HandleDomLoaded(const base::ListValue* args) {
 }
 
 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();
 }