Implement translation of EOpIndexDirectInterfaceBlock in OutputGLSL.
Implement translation of EOpIndexDirectInterfaceBlock in OutputGLSL.

BUG=angleproject:882
BUG=angleproject:1149

Change-Id: I5e0808dd3576339aa87aade3a349586d01b28f74
Reviewed-on: https://chromium-review.googlesource.com/297087
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Tested-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

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