Allow first uid in attribution chain as primary field

Test: bit statsd_test:*
Bug: 142108433
Change-Id: I6a2f8e6198765d4205dac95e5f54666496b78808
diff --git a/cmds/statsd/src/FieldValue.h b/cmds/statsd/src/FieldValue.h
index 6fc1e23..967fd32 100644
--- a/cmds/statsd/src/FieldValue.h
+++ b/cmds/statsd/src/FieldValue.h
@@ -261,6 +261,11 @@
     return Matcher(Field(tag, getSimpleField(field)), 0xff7f0000);
 }
 
+inline Matcher getFirstUidMatcher(int32_t atomId) {
+    int32_t pos[] = {1, 1, 1};
+    return Matcher(Field(atomId, pos, 2), 0xff7f7f7f);
+}
+
 /**
  * A wrapper for a union type to contain multiple types of values.
  *