Enable UFFD GC.

Bug: 160737021
Change-Id: Ic19c8764087607338963b0e5d351ff14f536dd20
Test: Presbumit
diff --git a/target/product/default_art_config.mk b/target/product/default_art_config.mk
index 752b199..1e28c80 100644
--- a/target/product/default_art_config.mk
+++ b/target/product/default_art_config.mk
@@ -115,4 +115,4 @@
     dalvik.vm.dex2oat-Xms=64m \
     dalvik.vm.dex2oat-Xmx=512m \
 
-PRODUCT_ENABLE_UFFD_GC := false  # TODO(jiakaiz): Change this to "default".
+PRODUCT_ENABLE_UFFD_GC := default