code: public GVRAnimation start(GVRAnimation animation) {
          if (animation.getRepeatCount() != 0) {
              animation.reset();
              mAnimations.add(animation);
          }
          animation.onStart();
          return animation;
      }
docs: Registers an animation with the engine: It will start running
  immediately.
  
  You will usually use {@link GVRAnimation#start(GVRAnimationEngine)}
  instead of this method:
  
  <pre>
  
  new GVRSomeAnimation(object, duration, parameter) //
  .setOnFinish(handler) //
  .start(animationEngine);
  </pre>
  
  reads better than
  
  <pre>
  
  animationEngine.start( //
  new GVRSomeAnimation(object, duration, parameter) //
  .setOnFinish(handler) //
  );
  </pre>
  
  @param animation
  an animation
  @return The animation that was passed in.