Make runtime display fallback when needed.

builtins/amp-ad.js

@@ -273,7 +273,6 @@ export function installAd(win) {
           this.viewer_.onVisibilityChanged(() => {
             this.sendEmbedInfo_(this.isInViewport());
           });
-
           return loadPromise(this.iframe_);
         });
       }

src/custom-element.js

@@ -934,6 +934,12 @@ export function createAmpElementProto(win, name, implementationClass) {
     // element, (b) some realyout is expected and (c) fallback condition would
     // be rare.
     this.classList.toggle('amp-notsupported', state);
+    if (state == true) {
+      const fallbackElement = this.getFallback();
+      if (fallbackElement) {
+        this.resources_.scheduleLayout(this, fallbackElement);
+      }
+    }
   };
 
   /**

test/functional/test-custom-element.js

@@ -798,8 +798,18 @@ describe('CustomElement Service Elements', () => {
   });
 
   it('toggleFallback should toggle unsupported class', () => {
+    const fallback = element.appendChild(createWithAttr('fallback'));
+    const resourcesSpy = sandbox.spy();
+    element.resources_ = {
+      scheduleLayout: function(el, fb) {
+        if (el == element && fb == fallback) {
+          resourcesSpy();
+        }
+      },
+    };
     element.toggleFallback(true);
     expect(element).to.have.class('amp-notsupported');
+    expect(resourcesSpy.callCount).to.equal(1);
 
     element.toggleFallback(false);
     expect(element).to.not.have.class('amp-notsupported');

test/manual/amp-ad.amp.html

@@ -39,5 +39,22 @@ <h1>AMP #0</h1>
       data-aax_pubname="abc123"
       data-aax_src="302">
   </amp-embed>
+  <h2>Doubleclick no ad with placeholder and fallback</h2>
+  <amp-ad width=300 height=200
+      type="doubleclick"
+      data-slot="/4119129/doesnt-exist"
+      >
+     <div class="adv-placeholder" placeholder>
+       <amp-anim width=16 height=16 src="//www.repstatic.it/cless-mobile/main/amp/2016-v1//img/loader.gif">
+           <amp-img placeholder width=16 height=16 src="//www.repstatic.it/cless-mobile/main/amp/2016-v1//img/loader.gif">
+         </amp-img>
+       </amp-anim>
+     </div>
+     <div fallback>
+       <a href="http://www.repubblica.it/sport/2016/02/09/news/app_rep-133068373/">
+         <amp-img placeholder width=300 height=100 src="//www.repstatic.it/cless-mobile/main/amp/2016-v1/img/adv-300-100.jpg">
+       </a>
+     </div>
+  </amp-ad>
 </body>
 </html>