Enable ART_USE_READ_BARRIER by default (test only)

This is only for cherrypick for performance testing.

Bug: 31528287
Bug: 12687968
Test: angler boot, test-art-host
Change-Id: I87ee7b4f16f6f7906421d9454381686ffe4c4554
diff --git a/build/Android.common_build.mk b/build/Android.common_build.mk
index 4c82506..f5a95fa 100644
--- a/build/Android.common_build.mk
+++ b/build/Android.common_build.mk
@@ -46,6 +46,9 @@
 $(info Disabling ART_BUILD_HOST_DEBUG)
 endif
 
+# Enable the read barrier by default.
+ART_USE_READ_BARRIER ?= true
+
 ART_CPP_EXTENSION := .cc
 
 ifndef LIBART_IMG_HOST_BASE_ADDRESS
diff --git a/build/art.go b/build/art.go
index ccaa11d..12f358b 100644
--- a/build/art.go
+++ b/build/art.go
@@ -58,7 +58,7 @@
 		asflags = append(asflags, "-DART_HEAP_POISONING=1")
 	}
 
-	if envTrue(ctx, "ART_USE_READ_BARRIER") {
+	if !envFalse(ctx, "ART_USE_READ_BARRIER") {
 		// Used to change the read barrier type. Valid values are BAKER, BROOKS, TABLELOOKUP.
 		// The default is BAKER.
 		barrierType := envDefault(ctx, "ART_READ_BARRIER_TYPE", "BAKER")
diff --git a/test/etc/run-test-jar b/test/etc/run-test-jar
index c525b2b..5e0ac92 100755
--- a/test/etc/run-test-jar
+++ b/test/etc/run-test-jar
@@ -43,7 +43,7 @@
 SECONDARY_DEX=""
 TIME_OUT="gdb"  # "n" (disabled), "timeout" (use timeout), "gdb" (use gdb)
 # Value in seconds
-if [ "$ART_USE_READ_BARRIER" = "true" ]; then
+if [ "$ART_USE_READ_BARRIER" != "false" ]; then
   TIME_OUT_VALUE=2400  # 40 minutes.
 else
   TIME_OUT_VALUE=1200  # 20 minutes.
diff --git a/test/run-test b/test/run-test
index 37eefb3..8ec3ca8 100755
--- a/test/run-test
+++ b/test/run-test
@@ -713,7 +713,7 @@
     #
     # TODO: Enable Checker when read barrier support is added to more
     # architectures (b/12687968).
-    if [ "x$ART_USE_READ_BARRIER" = xtrue ]                    \
+    if [ "x$ART_USE_READ_BARRIER" != xfalse ]                  \
        && (([ "x$host_mode" = "xyes" ]                         \
             && ! arch_supports_read_barrier "$host_arch_name") \
            || ([ "x$target_mode" = "xyes" ]                    \