Frameworks/base: Wall Werror in media/tests

Turn on -Wall -Werror in media/tests. Fix warnings.

Change-Id: I7177e795d4896f62dfa0b0a5990386e564763384
diff --git a/media/tests/players/Android.mk b/media/tests/players/Android.mk
index adf0d30..7ab6458 100644
--- a/media/tests/players/Android.mk
+++ b/media/tests/players/Android.mk
@@ -26,5 +26,6 @@
 LOCAL_MODULE:= invoke_mock_media_player
 LOCAL_MODULE_TAGS := tests eng
 
+LOCAL_CFLAGS += -Wall -Werror -Wunused -Wunreachable-code
 
 include $(BUILD_SHARED_LIBRARY)