D3D11: Reduce allocations in GenerateInitialTextureData. We can re-use the same info for each level of the texture. Also use fixed sized arrays for the subresource data structure. Bug: chromium:867089 Change-Id: Ie43886f708d1141fb80d30a78cabdd37dfbf6f94 Reviewed-on: https://chromium-review.googlesource.com/1149082 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>