The main functionality for NV12 texture support through EGL streams has
been added. Updates to the compiler, texture code, and stream code were
added to support binding to external D3D11 NV12 textures. An end2end test
was also added to test sampling of YUV textures and converting to RGB.
There is also a new script to convert BMP files to an NV12 texture ready
to load into D3D11 for testing purposes.

BUG=angleproject:1332

Change-Id: I39b6ec393ea338e2c843fb911acc1b36cd1158a0
Reviewed-on: https://chromium-review.googlesource.com/339454Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Ian Ewell <ewell@google.com>
Reviewed-on: https://chromium-review.googlesource.com/341254Reviewed-by: Ian Ewell <ewell@google.com>