EGL_KHR_stream is now implemented. Since the extension does not come with
any producers or consumers, it does not have much functionality and the
implementation is therefore very simple (validation layers and a new
object to store some attributes). This however add the groundwork to add
the appropriate consumer and producer extensions to stream D3D NV12
textures directly into ANGLE which will significantly improve video
performance on Chromium on D3D-based platforms.

BUG=angleproject:1332

Change-Id: Ie240c73869f5098d1215cc5e27aa5decd06c3ed1
Reviewed-on: https://chromium-review.googlesource.com/330003
Commit-Queue: Ian Ewell <ewell@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>