*DO NOT SUBMIT* Allow screenshots through 3rd party apps

This is for internal use only. Do not submit as a patch
for the general public as it has security holes.

For emulator instances where screencap does not work,
one can use this patch to allow 3rd party applications
to take a screenshot. It uses the same code as HiearchyViewer
but with ParcelFileDescriptors instead. The client side
should make the call on a separate thread from the reader
of the PFD so that the app does not get blocked.

Change-Id: I5bfb210e07aacc56e46e87cbe88ed31e73c61f83