Initialize TextureState::usage.
Initialize TextureState::usage.

This was probably omittted some time ago, and was showing up as
garbage in the debugger in some cases.

BUG=angleproject:1260

Change-Id: Ifca5243d0c94e7659a2245e327a72eed9dd918ab
Reviewed-on: https://chromium-review.googlesource.com/327401
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Reviewed-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>
Commit-Queue: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ecoal95/angle,ecoal95/angle,mikolalysenko/angle,mikolalysenko/angle,ppy/angle,ecoal95/angle,domokit/waterfall,ppy/angle,ppy/angle,ecoal95/angle,domokit/waterfall,MSOpenTech/angle,mikolalysenko/angle,MSOpenTech/angle,mikolalysenko/angle,ppy/angle,MSOpenTech/angle,ecoal95/angle,MSOpenTech/angle