facebook/buck — pull request #205 by jhansche (2014-10-14 19:41:04+00:00)
Title: Error in aapt_package when prebuilt AAR does not include any `res` files

If a prebuild AAR file contains an *empty* `res/` directory, the
directory does not get created in the `__unpack_*#aar_unzip__/res/`
location. This causes the `aapt` tool to fail with error:

ERROR: resource directory 'buck-out/bin/__unpack_#aar_unzip__/res' does not exist

In the `AndroidPrebuiltAarGraphEnhancer` class, there is a step
that accounts for a similar error on the `assets` directory:

steps.add(new MkdirStep(getAssetsDirectory()));

Adding a similar step for the `res` directory resolves the error.