Fix array.length() to return a signed integer array.length() should return a signed integer as specified in ESSL 3.00 section 4.1.9, not unsigned. Fix this and add a simple unit test - the dEQP tests included in WebGL conformance are built in a way that they don't catch the issue. TEST=angle_unittests BUG=angleproject:972 Change-Id: I1389f51751a6a25c1681f57ac3d2d52f31ecc8fb Reviewed-on: https://chromium-review.googlesource.com/266991 Reviewed-by: Olli Etuaho <oetuaho@nvidia.com> Tested-by: Olli Etuaho <oetuaho@nvidia.com>