Add unsigned literal support to GLSL output
Add unsigned literal support to GLSL output

BUG=angleproject:964

Change-Id: I8eb3cfd8d49beded4ac55ead97b50c7691e4980a
Reviewed-on: https://chromium-review.googlesource.com/263710
Tested-by: Olli Etuaho <38ae6c0e2772a20e8e989f80cb8c99d274e44242@nvidia.com>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

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