This is essentially a reland of 9cf9bcbe

This code always allocates a new memory buffer for the texture memory,
picks a load function to copy/convert the input data into it, and the
uploads.

In the case where the input format matches the upload format we should
be able to skip the allocation and copy and be much happier.

Change-Id: I3c1a0ab34be91c7d39eb2d0866029d01352b6056
Reviewed-on: https://chromium-review.googlesource.com/325526
Tryjob-Request: John Bauman <jbauman@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>