ESSL and GLSL are not consistent on invariant matching in vertex shader
and fragment shader. See the following rules:
ESSL 1.00 - input and output must match
ESSL 3.00 - only output, inputs cannot be declared as invariant.

GLSL 1.10.59 - does not exist
GLSL 1.20.8  - input and output must match
GLSL 1.30.10 - input and output must match
GLSL 1.40.8  - input and output must match
GLSL 1.50.11 - input and output must match
GLSL 3.30.6  - input and output must match
GLSL 4.00.9  - input and output must match
GLSL 4.10.6  - input and output must match
GLSL 4.20.11 - input can omit invariant
GLSL 4.30.8  - input can omit invariant
GLSL 4.40.9  - input can omit invariant
GLSL 4.50.5  - input can omit invariant

Since GLSL 4.20, invariant qualifier description were changed to:
"
Only variables output from a shader (including those that are then input
to a subsequent shader) can be candidates for invariance. This includes
user-defined output variables and the built-in output variables. As only
outputs need be declared with invariant, an output from one shader stage
will still match an input of a subsequent stage without the input being
declared as invariant.
"
It's not very clear if input in fragment can be declared as invariant.
Mesa driver disallows use of input declared as invariant in fragment
shader, while other drivers may allow it.

In ESSL 3.00, inputs cannot be declared as invariant. ANGLE should
follow this rule for GLSL >= 4.20.

BUG=chromium:639760

Change-Id: I7f7a07401381ac970488b69752f6d50d4f19d31f
Reviewed-on: https://chromium-review.googlesource.com/400005Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>