This test checks for OES_texture_half_float, but it's trying to use a
16F texture as a color buffer so it should be checking for
EXT_color_buffer_half_float.

Since EXT_color_buffer_half_float requires more format support (e.g.
R16F, RG16F, RGB16F) than OES_texture_half_float, it's possible for an
implementation to support one extension and not the other. D3D11 Feature
Level 9_3 does this.

Change-Id: I40fb38aa3f419be2606464bd0476cd064afe90fa
Reviewed-on: https://chromium-review.googlesource.com/319642Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Austin Kinross <aukinros@microsoft.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>