Fix Bitmap parceling through ashmem.

Fixes a bug where the Bitmap parceling code was unable to deal with
sending bitmaps through Parcels that disallow file descriptors.
Uses extended functionality of the Parcel blob interface to pass
buffers around more efficiently while adapting to whether FDs
are allowed.

Bug: 21428802
Change-Id: If24926f4388d29aa2aac627000436beb015edcb9