UniformBufferTest: fix invalid uniform index
UniformBufferTest: fix invalid uniform index

To get the index value of an uniform or uniform block, the Spec suggested way
is to enumerate according to its name. There is no mention that index has any
correspondence regarding the order of uniforms in shader source code.

BUG=angleproject:1622
BUG=angleproject:1543

Change-Id: I76dbf0ef05f89cd93ea2bdaf93a47f0f5d318f87
Reviewed-on: https://chromium-review.googlesource.com/497976
Commit-Queue: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

MSOpenTech/angle,ppy/angle,MSOpenTech/angle,ecoal95/angle,ecoal95/angle,ppy/angle,MSOpenTech/angle,ecoal95/angle,ecoal95/angle,ppy/angle,ppy/angle,ecoal95/angle,MSOpenTech/angle