Prepare for removal of legacy-test from default targets

In preparation for removing junit classes from the Android API
the legacy-test target will be removed from the
TARGET_DEFAULT_JAVA_LIBRARIES. This change adds explicit
dependencies on junit and/or legacy-android-test to ensure that
modules will compile properly once it is removed.

Bug: 30188076
Test: make checkbuild
Change-Id: Ibff876026420ae1de86897d928247895a182b50c
diff --git a/tests/Android.mk b/tests/Android.mk
index 8a8113b..f4b8256 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -22,7 +22,8 @@
         android-support-v4 \
         guava \
         mockito-target \
-        platform-test-annotations
+        platform-test-annotations \
+        legacy-android-test
 
 LOCAL_SRC_FILES := \
         $(call all-java-files-under, src) \