Add overlayable test resource for launcher3

Test: make RunLauncherRoboTests
Change-Id: I36b4869d44e8896ef59dce6c554ef94a1fe4d9ec
diff --git a/robolectric_tests/Android.mk b/robolectric_tests/Android.mk
index a57b97a..62915f2 100644
--- a/robolectric_tests/Android.mk
+++ b/robolectric_tests/Android.mk
@@ -46,6 +46,8 @@
 LOCAL_JAVA_LIBRARIES := \
     LauncherRoboTests
 
+LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/res
+
 LOCAL_TEST_PACKAGE := Launcher3
 
 LOCAL_INSTRUMENT_SOURCE_DIRS := $(dir $(LOCAL_PATH))../src \