code: public void setLayerInset(int index, int l, int t, int r, int b) {
          setLayerInsetInternal(index, l, t, r, b, UNDEFINED_INSET, UNDEFINED_INSET);
      }
docs: Specifies the insets in pixels for the drawable at the specified index.
  
  @param index the index of the drawable to adjust
  @param l     number of pixels to add to the left bound
  @param t     number of pixels to add to the top bound
  @param r     number of pixels to subtract from the right bound
  @param b     number of pixels to subtract from the bottom bound
  @attr ref android.R.styleable#LayerDrawableItem_left
  @attr ref android.R.styleable#LayerDrawableItem_top
  @attr ref android.R.styleable#LayerDrawableItem_right
  @attr ref android.R.styleable#LayerDrawableItem_bottom