Fix leak in the demo app

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=199448766

demos/main/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java

@@ -136,6 +136,7 @@ public class PlayerActivity extends Activity
 
   private DataSource.Factory mediaDataSourceFactory;
   private SimpleExoPlayer player;
+  private FrameworkMediaDrm mediaDrm;
   private MediaSource mediaSource;
   private DefaultTrackSelector trackSelector;
   private DefaultTrackSelector.Parameters trackSelectorParameters;
@@ -487,8 +488,9 @@ public class PlayerActivity extends Activity
             keyRequestPropertiesArray[i + 1]);
       }
     }
-    return new DefaultDrmSessionManager<>(
-        uuid, FrameworkMediaDrm.newInstance(uuid), drmCallback, null, multiSession);
+    releaseMediaDrm();
+    mediaDrm = FrameworkMediaDrm.newInstance(uuid);
+    return new DefaultDrmSessionManager<>(uuid, mediaDrm, drmCallback, null, multiSession);
   }
 
   private void releasePlayer() {
@@ -502,6 +504,23 @@ public class PlayerActivity extends Activity
       mediaSource = null;
       trackSelector = null;
     }
+    releaseMediaDrm();
+  }
+
+  private void releaseMediaDrm() {
+    if (mediaDrm != null) {
+      mediaDrm.release();
+      mediaDrm = null;
+    }
+  }
+
+  private void releaseAdsLoader() {
+    if (adsLoader != null) {
+      adsLoader.release();
+      adsLoader = null;
+      loadedAdTagUri = null;
+      playerView.getOverlayFrameLayout().removeAllViews();
+    }
   }
 
   private void updateTrackSelectorParameters() {
@@ -576,15 +595,6 @@ public class PlayerActivity extends Activity
     }
   }
 
-  private void releaseAdsLoader() {
-    if (adsLoader != null) {
-      adsLoader.release();
-      adsLoader = null;
-      loadedAdTagUri = null;
-      playerView.getOverlayFrameLayout().removeAllViews();
-    }
-  }
-
   // User controls
 
   private void updateButtonVisibilities() {