Add Google-style StringPrintf.

Change-Id: If333c28b8ed047346a2dd85e591c4bedbab874cc
diff --git a/libutils/tests/Android.mk b/libutils/tests/Android.mk
index 03d5342..ce288ca 100644
--- a/libutils/tests/Android.mk
+++ b/libutils/tests/Android.mk
@@ -30,6 +30,7 @@
     Looper_test.cpp \
     LruCache_test.cpp \
     String8_test.cpp \
+    stringprintf_test.cpp \
     Unicode_test.cpp \
     Vector_test.cpp \