Reinstate non-static useExtensionRenderers method

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=193970940

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

@@ -35,8 +35,6 @@ import java.io.File;
  */
 public class DemoApplication extends Application {
 
-  public static final boolean USE_EXTENSION_RENDERERS = "withExtensions".equals(BuildConfig.FLAVOR);
-
   private static final String DOWNLOAD_ACTION_FILE = "actions";
   private static final String DOWNLOAD_CONTENT_DIRECTORY = "downloads";
 
@@ -63,6 +61,11 @@ public class DemoApplication extends Application {
     return new DefaultHttpDataSourceFactory(userAgent, listener);
   }
 
+  /** Returns whether extension renderers should be used. */
+  public boolean useExtensionRenderers() {
+    return "withExtensions".equals(BuildConfig.FLAVOR);
+  }
+
   /** Returns the download {@link Cache}. */
   public synchronized Cache getDownloadCache() {
     if (downloadCache == null) {

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

@@ -381,7 +381,7 @@ public class PlayerActivity extends Activity
       boolean preferExtensionDecoders =
           intent.getBooleanExtra(PREFER_EXTENSION_DECODERS_EXTRA, false);
       @DefaultRenderersFactory.ExtensionRendererMode int extensionRendererMode =
-          DemoApplication.USE_EXTENSION_RENDERERS
+          ((DemoApplication) getApplication()).useExtensionRenderers()
               ? (preferExtensionDecoders ? DefaultRenderersFactory.EXTENSION_RENDERER_MODE_PREFER
               : DefaultRenderersFactory.EXTENSION_RENDERER_MODE_ON)
               : DefaultRenderersFactory.EXTENSION_RENDERER_MODE_OFF;