Add ArtUseReadBarrier to ProductVariables.

Bug: 33492005
Test: top-level angler build.
Change-Id: Ib04284bac923a143038655d495bcbacaabf61440
diff --git a/android/config.go b/android/config.go
index 8f531cc..7d268fc 100644
--- a/android/config.go
+++ b/android/config.go
@@ -435,6 +435,10 @@
 	}
 }
 
+func (c *config) ArtUseReadBarrier() bool {
+	return Bool(c.ProductVariables.ArtUseReadBarrier)
+}
+
 func (c *deviceConfig) Arches() []Arch {
 	var arches []Arch
 	for _, target := range c.config.Targets[Device] {