OES_sample_variables extension incorrect use of #extension

[tsuoranta]

OES_sample_variables says:

Including the following line in a shader can be used to control the language features described in this extension: #extension GL_OES_sample_variables

Meanwhile, my intrepretation of ESSL 3.00 is that : <behavior> must always follow.

[pdaniell-nv]

Yes, this is wrong. Will you propose a PR to fix it?