Add menu mode plumbing for WebVR mode.

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 f93a98ba208b8ab3cd9aff3d57c163d57072b0dc..f200640ecb50043523e2da5db04f65496be3ef2c 100644
--- a/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
+++ b/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
@@ -15,7 +15,7 @@ api.Command = {
   'REMOVE_ELEMENT': 2,
   'ADD_ANIMATION': 3,
   'REMOVE_ANIMATION': 4,
-  'UPDATE_BACKGROUND': 5
+  'CONFIGURE_SCENE': 5
 };
 
 /**
@@ -540,6 +540,56 @@ api.Animation = class {
 };
 
 /**
+ * Scene configuration class. Use this object to generate the payload of a
+ * CONFIGURE_SCENE command.
+ * @struct
+ */
+api.SceneConfiguration = class {
+  constructor() {
+    /** @private {!Object} */
+    this.properties = {};
+  }
+
+  getCommandPayload() {
+    return this.properties;
+  }
+
+  /**
+   * Set the background color of the scene.
+   * @param {{r: number, b: number, g: number, a: number}} color
+   */
+  setBackgroundColor(color) {
+    this.properties.backgroundColor = color;
+  }
+
+  /**
+   * Set the radius of the background-bounding sphere.
+   * @param {number} distance
+   */
+  setBackgroundDistance(distance) {
+    this.properties.backgroundDistance = distance;
+  }
+
+  /**
+   * Enable or disable rendering of the laser and reticle.
+   * @param {boolean} enabled
+   */
+  setCursorEnabled(enabled) {
+    this.properties.drawCursor = enabled;
+  }
+
+  /**
+   * Enable or disable rendering of WebVR content in the foreground. Rendering
+   * defaults to enable when on a WebVR page. This property allows rendering to
+   * be disabled, for purposes of showing an alternate UI (such as a menu).
+   * @param {boolean} enabled
+   */
+  setWebVrRenderingEnabled(enabled) {

[tiborg, 2017/03/16 19:40:23]

Maybe call it setShowWebVrPresentation or so? Since WebVR is still rendered.

[cjgrant, 2017/03/20 15:34:57]

Now that this controls rendering of WebVR vs UI and cursor, I like the original
name better.  Or, it could be setWebVrRenderingModeEnabled(), to show it has a
broader impact...  Thoughts?

[tiborg, 2017/03/20 15:56:08]

setWebVrRenderingModeEnabled() sounds good to me.

[cjgrant, 2017/03/20 17:57:22]

Done.

+    this.properties.drawWebVr = enabled;
+  }
+};
+
+/**
  * Abstract class handling webui command calls from native.  The UI must
  * subclass this and override the handlers.
  * @abstract