[DO NOT MERGE] Fix wallpaper cropping bugs

- take into account that image decoder might not
respect inSampleSize
- check rounded values so we don't have crop rects
that lie outside a bitmap's dimensions
- correctly set initial scale on bitmaps that are
larger than the screen size
- switch to using asynctask when setting wallpaper
dimensions
(cherry picked from commit e39c9a95)

Change-Id: I43372f0bff37f139c8bc83f9956a967d0b4a8708