Optimizations for AppCompat + VDC integration

- Only installs the delegate if we need it (< API 21)
- Use a Drawable cache for delegate created drawables
  (ala Resources).
- Use an instance cache for TintContextWrapper. Previously
  we were creating one for nearly view, which also meant that
  we were creating a new Theme instance for every view.

BUG: 26451702

Change-Id: I36af2f36a57de109710681877ea67c1e4ea652a5
2 files changed