Clean up VR Shell mode transitions (and fix potential webvr startup race).

chrome/browser/android/vr_shell/ui_interface.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/android/vr_shell/ui_interface.h"
 
 #include "chrome/browser/ui/webui/vr_shell/vr_shell_ui_message_handler.h"
 #include "url/gurl.h"
 
 namespace vr_shell {
 
-UiInterface::UiInterface() {
-  SetMode(Mode::STANDARD);
+UiInterface::UiInterface(Mode initial_mode) {
+  SetMode(initial_mode);
 }
 
 UiInterface::~UiInterface() {}
 
 void UiInterface::SetMode(Mode mode) {
   mode_ = mode;
   updates_.SetInteger("mode", static_cast<int>(mode));
   FlushUpdates();
 }
 
@@ skipping 29 matching lines @@
 }
 
 void UiInterface::FlushUpdates() {
   if (loaded_ && handler_) {
     handler_->SendCommandToUi(updates_);
     updates_.Clear();
   }
 }
 
 }  // namespace vr_shell