code: public ViewPropertyAnimator setDuration(long duration) {
          if (duration < 0) {
              throw new IllegalArgumentException("Animators cannot have negative duration: " +
                      duration);
          }
          mDurationSet = true;
          mDuration = duration;
          return this;
      }
docs: Sets the duration for the underlying animator that animates the requested properties.
  By default, the animator uses the default value for ValueAnimator. Calling this method
  will cause the declared value to be used instead.
  @param duration The length of ensuing property animations, in milliseconds. The value
  cannot be negative.
  @return This object, allowing calls to methods in this class to be chained.