Adds OPENGLES_NULL configuration
and selects between OPENGL and OPENGLES based on whether building for Android.

Also 2 small changes to get the newly enabled tests to pass on N5X:
1. Require GL_EXT_texture_storage in TexSubImage test
2. Limit numVertexUniforms and numFragmentUniforms to 64 in MatrixUniforms test

BUG=675997
Change-Id: I5439e5fb7e93b3a928f12594761115d56f60d81b
Reviewed-on: https://chromium-review.googlesource.com/748522
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>