Ensure that the web contents trying to access native VR Shell is the webcontents we created.

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 a4d28369835c244b23e72c509e30c09af8cd6558..5edcf5601085ad683416dc9d7bb2b79e013693e5 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
@@ -18,7 +18,7 @@ VrShellUIMessageHandler::VrShellUIMessageHandler() {}
 VrShellUIMessageHandler::~VrShellUIMessageHandler() {}
 
 void VrShellUIMessageHandler::RegisterMessages() {
-  vr_shell_ = vr_shell::VrShell::GetWeakPtr();
+  vr_shell_ = vr_shell::VrShell::GetWeakPtr(web_ui()->GetWebContents());
 
   web_ui()->RegisterMessageCallback(
       "domLoaded", base::Bind(&VrShellUIMessageHandler::HandleDomLoaded,