Previously, the order of styles outputted by this module was
arbitrary, based on the order of the feature files passed in.
This was not how it was intended to work - the ResourceLoaderSkinModule
should be aware of the correct ordering.
In the case of normalize for example - it should always be the first
file output.
The implementation is adapted to check for valid features once in
the constructor and to also consider a DEFAULT_FEATURES value has been
set.
We use the FEATURE_FILES constant to determine
the order of CSS output.
This is all documented in the class.
Bug: T269618
Change-Id: Iecbf11b5f09882e55d694651210d6d132d3cd412
4a287f9217