Add timeout support to __system_property_wait.

Bug: http://b/35201172
Test: ran tests
Change-Id: I3a78813bf3cd50d1b308ecb3c742f923606c0cc4
diff --git a/tests/system_properties_test.cpp b/tests/system_properties_test.cpp
index 39734d7..ff97549 100644
--- a/tests/system_properties_test.cpp
+++ b/tests/system_properties_test.cpp
@@ -402,7 +402,9 @@
         __system_property_update(pi, "value2", 6);
     });
 
-    __system_property_wait(pi, serial);
+    uint32_t new_serial;
+    __system_property_wait(pi, serial, &new_serial, nullptr);
+    ASSERT_GT(new_serial, serial);
 
     char value[PROP_VALUE_MAX];
     ASSERT_EQ(6, __system_property_get("property", value));