code: ChildDrawable addLayer(Drawable dr, int[] themeAttrs, int id,
                             int left, int top, int right, int bottom) {
          final ChildDrawable childDrawable = createLayer(dr);
          childDrawable.mId = id;
          childDrawable.mThemeAttrs = themeAttrs;
          if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT)
              childDrawable.mDrawable.setAutoMirrored(isAutoMirrored());
          childDrawable.mInsetL = left;
          childDrawable.mInsetT = top;
          childDrawable.mInsetR = right;
          childDrawable.mInsetB = bottom;
  
          addLayer(childDrawable);
  
          mLayerState.mChildrenChangingConfigurations |= dr.getChangingConfigurations();
          dr.setCallback(this);
  
          return childDrawable;
      }
docs: Add a new layer to this drawable. The new layer is identified by an id.
  
  @param dr         The drawable to add as a layer.
  @param themeAttrs Theme attributes extracted from the layer.
  @param id         The id of the new layer.
  @param left       The left padding of the new layer.
  @param top        The top padding of the new layer.
  @param right      The right padding of the new layer.
  @param bottom     The bottom padding of the new layer.