Switch the default read barrier type to a Baker one.

For automated testing.

Bug: 12687968
Change-Id: I831d6e45e4729f0dd3cf178d02af511a32cc9777
diff --git a/runtime/read_barrier_c.h b/runtime/read_barrier_c.h
index a2c4c36..88bda3a 100644
--- a/runtime/read_barrier_c.h
+++ b/runtime/read_barrier_c.h
@@ -26,9 +26,9 @@
 // table-lookup read barriers.
 
 #ifdef ART_USE_READ_BARRIER
-// #define USE_BAKER_READ_BARRIER
+#define USE_BAKER_READ_BARRIER
 // #define USE_BROOKS_READ_BARRIER
-#define USE_TABLE_LOOKUP_READ_BARRIER
+// #define USE_TABLE_LOOKUP_READ_BARRIER
 #endif
 
 #if defined(USE_BAKER_READ_BARRIER) || defined(USE_BROOKS_READ_BARRIER)