Control visibility of 2D VR menu buttons using native state.

chrome/browser/resources/vr_shell/vr_shell_ui_api.js

Index: chrome/browser/resources/vr_shell/vr_shell_ui_api.js
diff --git a/chrome/browser/resources/vr_shell/vr_shell_ui_api.js b/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
index 976b616aa26e65e61e1166b51ab6887e442ba53b..085af162bf2600f6efc5969974201dd2424f0cea 100644
--- a/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
+++ b/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
@@ -70,7 +70,18 @@ var api = (function() {
     'HISTORY_FORWARD': 1,
     'RELOAD': 2,
     'ZOOM_OUT': 3,
-    'ZOOM_IN': 4,
+    'ZOOM_IN': 4
+  });
+
+  /**
+   * Enumeration of modes that can be specified by the native side.
+   * @enum {number}
+   * @const
+   */
+  var Mode = Object.freeze({
+    'UNKNOWN': -1,
+    'STANDARD': 0,
+    'WEB_VR': 1
   });
 
   /**
@@ -268,6 +279,7 @@ var api = (function() {
     Easing: Easing,
     Command: Command,
     Action: Action,
+    Mode: Mode,
     getContentElementId: getContentElementId,
     UiElement: UiElement,
     UiElementUpdate: UiElementUpdate,