Trivial scanf benchmarks.

Bug: http://b/68672236
Test: ran benchmarks
Change-Id: I96514be5e67969b65205e953051c524be3626ec4
diff --git a/benchmarks/tests/interface_test.cpp b/benchmarks/tests/interface_test.cpp
index 3020c27..64629e6 100644
--- a/benchmarks/tests/interface_test.cpp
+++ b/benchmarks/tests/interface_test.cpp
@@ -298,6 +298,9 @@
     "BM_stdio_printf_d/iterations:1\n"
     "BM_stdio_printf_literal/iterations:1\n"
     "BM_stdio_printf_s/iterations:1\n"
+    "BM_stdio_scanf_d/iterations:1\n"
+    "BM_stdio_scanf_maps/iterations:1\n"
+    "BM_stdio_scanf_s/iterations:1\n"
     "BM_stdlib_malloc_free/8/iterations:1\n"
     "BM_stdlib_malloc_free/64/iterations:1\n"
     "BM_stdlib_malloc_free/512/iterations:1\n"