The EXT_color_buffer_half_float spec states:

    If OES_texture_half_float is supported, textures created with:

        <internalformat> = RGBA
        <format> = RGBA
        <type> = HALF_FLOAT_OES

    are renderable.

But WebGL content relies on being able to render to both RGB and RGBA unsized
HALF_FLOAT_OES textures.

Framebuffers may still return unsupported for this format.

BUG=941671

Change-Id: I42d909d26508b9cdf7cda6d1dc025b0e2ed87732
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1523530Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
(cherry picked from commit 979f3bbe)
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1539261Reviewed-by: Geoff Lang <geofflang@chromium.org>