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

chrome/browser/android/vr_shell/vr_web_contents_observer.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/vr_web_contents_observer.h"
 
 #include "chrome/browser/android/vr_shell/ui_interface.h"
 #include "content/public/browser/navigation_handle.h"
 
 namespace vr_shell {
@@ skipping 28 matching lines @@
 }
 
 void VrWebContentsObserver::DidFinishNavigation(
     content::NavigationHandle* navigation_handle) {
   ui_interface_->SetURL(navigation_handle->GetURL());
 }
 
 void VrWebContentsObserver::DidToggleFullscreenModeForTab(
     bool entered_fullscreen, bool will_cause_resize) {
   // TODO(amp): Use will_cause_resize to signal ui of pending size changes.
-  int mode = ui_interface_->GetMode();
-  if (entered_fullscreen && mode == UiInterface::Mode::STANDARD) {
-    ui_interface_->SetMode(UiInterface::Mode::CINEMA);
-  }
-  if (!entered_fullscreen && mode == UiInterface::Mode::CINEMA) {
-    ui_interface_->SetMode(UiInterface::Mode::STANDARD);
-  }
+  ui_interface_->SetCinemaMode(entered_fullscreen);
 }
 
 }  // namespace vr_shell