If GL_OES_texture_npot isn't active then ANGLE currently prevents
calls to glTexSubImage2D with:
- level > 0
- width/height NPOT

This isn't correct. It is legitimate to supply data to a NPOT subregion of a
POT texture via glTexSubImage2D.

Fixes these dEQP tests on 9_3:
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.a8_2d
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.a8_cube
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.l8_2d
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.l8_cube
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.la88_2d
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.la88_cube
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgb565_2d
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgb565_cube
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgb888_2d
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgb888_cube
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgba4444_2d
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgba4444_cube
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgba5551_2d
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgba5551_cube
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgba8888_2d
dEQP-GLES2.functional.texture.specification.basic_texsubimage2d.rgba8888_cube

Change-Id: I5889a27edbfa807995fa20b16f36456f676b80fc
Reviewed-on: https://chromium-review.googlesource.com/304612Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Austin Kinross <aukinros@microsoft.com>
Tested-by: Jamie Madill <jmadill@chromium.org>