These are discouraged anyway, due to the fact that using them may
result in decoding on the UI thread. Now that they are ignored, the
images will still be decoded; they just will never have their
memory purged, meaning there could be a RAM penalty. This is
acceptable, since apps are encouraged to instead use inBitmap to
manage bitmap memory.
This incidentally fixes BUG:15390468 by converting purgeable index8
(e.g. gif) images to non purgeable.
Change-Id: Ieaf3ab25d28d93fb94bdaea1eb3bd762f163b09a
0aa39dc2dc