Fix an issue with separate invariant statement.
Fix an issue with separate invariant statement.

Basically we end up with an extra "invariant xxx ;;" on GL backend.

This is not handled correctly by Mac drivers and also out shader translator.

BUG=angle:776
TEST=webgl conformance on mac/windows

Change-Id: If32867efba64ab0d3e6e690155790b90d736439f
Reviewed-on: https://chromium-review.googlesource.com/225780
Tested-by: Zhenyao Mo <655bdf1d95ff956cd68886dd9e86ee5e987c9dbb@chromium.org>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

bsergean/angle,csa7mdm/angle,mlfarrell/angle,mrobinson/rust-angle,larsbergstrom/angle,vvuk/angle,mrobinson/rust-angle,csa7mdm/angle,ecoal95/angle,ppy/angle,mikolalysenko/angle,ppy/angle,MSOpenTech/angle,vvuk/angle,crezefire/angle,csa7mdm/angle,ecoal95/angle,nandhanurrevanth/angle,MSOpenTech/angle,mybios/angle,crezefire/angle,mybios/angle,ghostoy/angle,ghostoy/angle,ppy/angle,mybios/angle,larsbergstrom/angle,ecoal95/angle,bsergean/angle,mybios/angle,mikolalysenko/angle,ecoal95/angle,domokit/waterfall,mikolalysenko/angle,domokit/waterfall,mlfarrell/angle,mikolalysenko/angle,vvuk/angle,ecoal95/angle,mrobinson/rust-angle,bsergean/angle,nandhanurrevanth/angle,MSOpenTech/angle,vvuk/angle,mrobinson/rust-angle,bsergean/angle,mlfarrell/angle,larsbergstrom/angle,csa7mdm/angle,ghostoy/angle,larsbergstrom/angle,mrobinson/rust-angle,crezefire/angle,MSOpenTech/angle,nandhanurrevanth/angle,ghostoy/angle,crezefire/angle,nandhanurrevanth/angle,mlfarrell/angle,ppy/angle