Current screenshot: https://drive.google.com/a/google.com/file/d/0B7c8ZkXVwskDd1pocmo5dUdHcG8/view?usp=sharing

* Add a pair of methods to ApiCompatibilityUtils for
  grabbing storage size information.

* Add a small widget for displaying how much space is used
  compared to how large storage is.

* Add a way to select a filter for the downloads.  It's not
  currently hooked up to anything.

* Add a bunch of icons for the sections.

BUG=616324

Review-Url: https://codereview.chromium.org/2063983002
Cr-Commit-Position: refs/heads/master@{#401137}