The binding point of uniform blocks can be specified in shaders with
this CL. See spec ESSL 3.10, section 4.4.4, page 58 for more info.

dEQP-GLES31.functional.ubo.* still can't completely pass as
the missing of arrays-of-arrays feature. Neither can
dEQP-GLES31.functional.layout_binding.ubo.* due to the incomplete
implementation of program interface APIs.

TEST=angle_end2end_tests:UniformBufferTest
BUG=angleproject:1442

Change-Id: If95d468fc109834a132b9b817730d3fdc3a615da
Reviewed-on: https://chromium-review.googlesource.com/483848
Commit-Queue: Jie A Chen <jie.a.chen@intel.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>