skia: Fix command buffer support on the mac

skia: Fix command buffer support on the mac

The extension on the mac is .dylib, updated the name.

EGL.h isn't available on mac (unless we include skia_angle.h).
I've got a somewhat bad hack of defining the types that I need
to get this running.

GetProcedureAddress was somehow successfully grabbing gl
functions from another lib.  Removed this call, I copied it
from ANGLE impl, but it isn't required.

lib load path works differently, fixed in GYP

BUG=skia:2992

Review URL: https://codereview.chromium.org/1403153002