Make systemTime() abort on bad input.

There's no CHECK in libutils, sadly.

Bug: http://b/157167405
Test: treehugger
Change-Id: I1532bf80ba7fdafad016610be3c782b547417126
diff --git a/libutils/Android.bp b/libutils/Android.bp
index 0f7044a..ea39d34 100644
--- a/libutils/Android.bp
+++ b/libutils/Android.bp
@@ -246,6 +246,7 @@
         "String8_test.cpp",
         "String16_test.cpp",
         "StrongPointer_test.cpp",
+        "Timers_test.cpp",
         "Unicode_test.cpp",
         "Vector_test.cpp",
     ],