Teach ImageView to recycle internal drawables

Bug: 22289362

It's pretty common for ImageView#setBitmap to be called
repeatedly. Avoid re-creating the BitmapDrawable in this scenario
as that has high object churn of semi-expensive objects like
Paint.

Change-Id: Ib77719cd0366d02c1a42f774850bf3b9caa9c288
2 files changed