[varStore] Add subset_varidxes as method on VarStore

Lib/fontTools/subset/__init__.py

@@ -1674,7 +1674,7 @@ def _pruneGDEF(font):
 		_visit(font['GPOS'].table, otTables.Device, adder)
 
 	# Subset.
-	varidx_map = varStore.VarStore_subset_varidxes(store, usedVarIdxes)
+	varidx_map = store.subset_varidxes(usedVarIdxes)
 
 	# Map.
 	mapper = partial(_Device_mapVarIdx, mapping=varidx_map)

Lib/fontTools/varLib/varStore.py

@@ -1,6 +1,7 @@
 from __future__ import print_function, division, absolute_import
 from __future__ import unicode_literals
 from fontTools.misc.py23 import *
+from fontTools.ttLib.tables import otTables as ot
 from fontTools.varLib.models import supportScalar
 from fontTools.varLib.builder import (buildVarRegionList, buildVarStore,
 				      buildVarRegion, buildVarData,
@@ -172,3 +173,5 @@ def VarStore_subset_varidxes(self, varIdxes, optimize=True):
 		data.VarRegionIndex = [regionMap[i] for i in data.VarRegionIndex]
 
 	return varDataMap
+
+ot.VarStore.subset_varidxes = VarStore_subset_varidxes