WebGL validation for depthRange. Generate INVALID_OPERATION for depthRange(zNear, zFar) if zNear > zFar. Add corresponding test. BUG=angleproject:1816 Change-Id: I28b5876a74c9765c0eef1e0f6e5e96d0380586d0 Reviewed-on: https://chromium-review.googlesource.com/441207 Commit-Queue: Frank Henigman <fjhenigman@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>