title: Admob Interstitial closes existing activity
body: <p>When I display an Admob interstitial, it displays fine, and I have registered a listener to catch the onAdClosed event, but the problem is that I cannot actually do anything from that event that interacts with my UI because the interstitial has closed it all. </p>
  
  <p>I'm creating the interstitial like this:</p>
  
  <pre><code>    storyAd = new InterstitialAd(this);
      storyAd.setAdUnitId("ca-app-pub-xxxxxxxxxxxxxxxx");
      storyAd.setAdListener(new AdListener() {
          @Override
          public void onAdClosed() {
              super.onAdClosed();
              storyAd.loadAd(buildAdRequest());
              if (prevMusicPlaying) {
                  toggleAudio();
              }
              loadNextPage();
          }
      });
      storyAd.loadAd(buildAdRequest());
  </code></pre>
  
  <p>I have it in my manifest too:</p>
  
  <pre><code>    &lt;activity android:name="com.google.android.gms.ads.AdActivity"
          android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize"
          android:theme="@android:style/Theme.Translucent" /&gt;
  </code></pre>
  
  <p>The loadNextPage() call crashes because it tries to create a new fragment and add it to my activity, which it cannot do because the activity has been paused by the interstitial. So I just get this exception:</p>
  
  <pre><code>Caused by: java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
                        at android.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1328)
                        at android.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1346)
                        at android.app.FragmentManagerImpl.popBackStack(FragmentManager.java:488)
  </code></pre>
  
  <p>How can I make it so that the InterstitialAd doesn't interfere in any way with the existing UI. It took a very long time to get the existing UI working with the various activity/fragment gotchas.</p>