✨ [Story Preview] Allow all story pages and grid layers to be rendered in preview mode

extensions/amp-story/1.0/amp-story-grid-layer.js

@@ -64,6 +64,11 @@ export class AmpStoryGridLayer extends AmpStoryBaseLayer {
     return isPrerenderActivePage(element.parentElement);
   }
 
+  /** @override  */
+  static previewAllowed() {
+    return true;
+  }
+
   /** @param {!AmpElement} element */
   constructor(element) {
     super(element);

extensions/amp-story/1.0/amp-story-page.js

@@ -165,6 +165,11 @@ export class AmpStoryPage extends AMP.BaseElement {
     return isPrerenderActivePage(element);
   }
 
+  /** @override  */
+  static previewAllowed() {
+    return true;
+  }
+
   /** @param {!AmpElement} element */
   constructor(element) {
     super(element);

extensions/amp-story/1.0/test/test-amp-story-page.js

@@ -29,6 +29,7 @@ describes.realWin('amp-story-page', {amp: {extensions}}, (env) => {
   let html;
   let gridLayerEl;
   let page;
+  let story;
   let storeService;
   let isPerformanceTrackingOn;
 
@@ -67,7 +68,7 @@ describes.realWin('amp-story-page', {amp: {extensions}}, (env) => {
       };
     });
 
-    const story = win.document.createElement('amp-story');
+    story = win.document.createElement('amp-story');
     story.getImpl = () => Promise.resolve(mediaPoolRoot);
     // Makes whenUpgradedToCustomElement() resolve immediately.
     story.createdCallback = Promise.resolve();
@@ -713,4 +714,26 @@ describes.realWin('amp-story-page', {amp: {extensions}}, (env) => {
 
     expect(startMeasuringStub).to.not.have.been.called;
   });
+
+  it('should only allow the prerender visibility state if it is the first page', async () => {
+    const pageElement2 = win.document.createElement('amp-story-page');
+    const pageElement3 = win.document.createElement('amp-story-page');
+    story.appendChild(pageElement2);
+    story.appendChild(pageElement3);
+
+    expect(AmpStoryPage.prerenderAllowed(element)).to.be.true;
+    expect(AmpStoryPage.prerenderAllowed(pageElement2)).to.be.false;
+    expect(AmpStoryPage.prerenderAllowed(pageElement3)).to.be.false;
+  });
+
+  it('should always allow the preview visibility state', async () => {
+    const pageElement2 = win.document.createElement('amp-story-page');
+    const pageElement3 = win.document.createElement('amp-story-page');
+    story.appendChild(pageElement2);
+    story.appendChild(pageElement3);
+
+    expect(AmpStoryPage.previewAllowed(element)).to.be.true;
+    expect(AmpStoryPage.previewAllowed(pageElement2)).to.be.true;
+    expect(AmpStoryPage.previewAllowed(pageElement3)).to.be.true;
+  });
 });