Handle compressed texture formats in the emulated TextureStorage for TextureGL.
Handle compressed texture formats in the emulated TextureStorage for TextureGL.

BUG=angleproject:884

Change-Id: Id54d9ff2845af52807161e0b589d8b76cfba412d
Reviewed-on: https://chromium-review.googlesource.com/272424
Reviewed-by: Kenneth Russell <1ebccd90c2bc76de65b6f830f2128a91ed69fdfb@chromium.org>
Reviewed-by: Brandon Jones <303ddc8529a3012e7fb187d611f08537af0cc183@chromium.org>
Tested-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

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