Fixed XR Layer rendering race condition with session initialization and RenderState Update (#5489)

* Fixed XR Layer rendering race condition with session initialization and RenderState update.

* Execute enterVRSuccess after xrSession is fully initialized.

Author: zjm-meta

src/components/layer.js

@@ -367,7 +367,6 @@ module.exports.Component = registerComponent('layer', {
       return;
     }
     xrSession.requestReferenceSpace('local-floor').then(this.onRequestedReferenceSpace);
-    this.needsRedraw = true;
     this.layerEnabled = true;
     if (this.quadPanelEl) {
       this.quadPanelEl.object3D.visible = false;

src/core/scene/a-scene.js

@@ -299,19 +299,18 @@ class AScene extends AEntity {
           self.usedOfferSession |= useOfferSession;
           requestSession(xrMode, xrInit).then(
             function requestSuccess (xrSession) {
-              self.xrSession = xrSession;
-
               if (useOfferSession) {
                 self.usedOfferSession = false;
               }
 
               vrManager.layersEnabled = xrInit.requiredFeatures.indexOf('layers') !== -1;
               vrManager.setSession(xrSession).then(function () {
                 vrManager.setFoveation(rendererSystem.foveationLevel);
+                self.xrSession = xrSession;
+                self.systems.renderer.setWebXRFrameRate(xrSession);
+                xrSession.addEventListener('end', self.exitVRBound);
+                enterVRSuccess(resolve);
               });
-              self.systems.renderer.setWebXRFrameRate(xrSession);
-              xrSession.addEventListener('end', self.exitVRBound);
-              enterVRSuccess(resolve);
             },
             function requestFail (error) {
               var useAR = xrMode === 'immersive-ar';