Build and install the Testing Runtime APEX in ART device testing.

Replace the Debug Runtime APEX with the Testing Runtime APEX for ART
device testing.

This change does not change the behavior of ART device testing per se,
as test rules have not been updated (yet) to make use of the
additional files (ART gtests) included only in the Testing Runtime
APEX.

Test: ART (chroot-based) device testing
Bug: 129534335
Change-Id: I1b9dfcb9fe483584b4065908c1b2e24d19703b52
diff --git a/build/Android.common_path.mk b/build/Android.common_path.mk
index b0bd7fd..a78d489 100644
--- a/build/Android.common_path.mk
+++ b/build/Android.common_path.mk
@@ -150,9 +150,9 @@
 # Release Runtime APEX, included by default in "user" builds.
 RELEASE_RUNTIME_APEX := com.android.runtime.release
 # Debug Runtime APEX, included by default in "userdebug" and "eng"
-# builds and used in ART device testing and benchmarking.
+# builds and used in ART device benchmarking.
 DEBUG_RUNTIME_APEX := com.android.runtime.debug
-# Testing Runtime APEX (not used yet).
+# Testing Runtime APEX, used in ART device testing.
 TESTING_RUNTIME_APEX := com.android.runtime.testing
 
 endif # ART_ANDROID_COMMON_PATH_MK