This makes ANGLE to follow GLSL ES 3.00.6 spec section 12.46. The spec
requires that all attributes are taken into account when checking for
aliasing, regardless of if they are active or not. WebGL 2.0 spec was
also recently changed to reflect GLSL ES 3.00.6 correctly. Aliasing
checks for GLSL ES 1.00 shaders are left as-is.

BUG=chromium:829541
TEST=angle_end2end_tests, WebGL conformance tests

Change-Id: I71c36ac123f18dadf075e81f93af29321c15136b
Reviewed-on: https://chromium-review.googlesource.com/1005077Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>