public static void init(final Resources resources) {
    if (sPlaceholderDrawable == null) {
      sPlaceholderDrawable = resources.getDrawable(R.color.placeholder);
    }
    if (sErrorDrawable == null) {
      sErrorDrawable = resources.getDrawable(R.color.error);
    }
  }
Holds static drawables used in the sample app.

<p>Using static set of drawables allows us to easily determine state of image request by simply
looking what kind of drawable is passed to image view.
samples/comparison/src/main/java/com/facebook/samples/comparison/Drawables.java