Add XtsMediaTestCases.apk to google-tests.zip

Need to add our Xts Media tests to the test package, so that we can
execute those tests with our nightly regression.

Previous cl (716634) for this was rolled back, as it didn't conditionally
check for the presence of vendor/xts to the build environment before adding
the dependency. This cl corrects that, and verified by removing vendor/xts
from the build environment, and validated that both make tests built
successfully, and the generated google-tests.zip was created as expected
(only missing XtsMediaTestCases.apk).

Bug: 22094009
Change-Id: Ia4e5ee0abbaf1e0efc591d6db34aa3f35ac62330

tests/Android.mk

@@ -24,6 +24,19 @@ WIDEVINE_TEST_MAKE_TARGETS := \
     request_license_test \
     timer_unittest \
 
+LOCAL_XTS_PATH := vendor/xts/xts-tests/tests/media/Android.mk
+# Need to make sure LOCAL_XTS_PATH actually exists in the build environment.
+# The gnu wildcard function will return a space-separated list of existing
+# files that match one of the given file name patterns. If no existing file
+# name matches, then that pattern is omitted from the output of the wildcard
+# function. For more details, see:
+# https://www.gnu.org/software/make/manual/html_node/Wildcard-Function.html
+_xts_makefile := $(strip $(wildcard $(LOCAL_XTS_PATH)))
+ifdef _xts_makefile
+    WIDEVINE_TEST_MAKE_TARGETS += XtsMediaTestCases
+    include $(_xts_makefile)
+endif
+
 # Call the makefiles for all our tests used in TradeFederation
 MODULAR_DRM_PATH := vendor/widevine/libwvdrmengine
 include $(MODULAR_DRM_PATH)/test/gmock/Android.mk