Only set UI warning on hidden API dark greylist

The framework might show a toast notification on access to greylisted
hidden APIs. Only show this warning on dark greylist so as to not spam
early testers.

Bug: 64382372
Test: make
Change-Id: I8b5f7b4938e0f238c513e37d7db06856b966802f
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 5a3a6f0..25d83df 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -268,6 +268,7 @@
       do_hidden_api_checks_(true),
       pending_hidden_api_warning_(false),
       dedupe_hidden_api_warnings_(true),
+      always_set_hidden_api_warning_flag_(false),
       dump_native_stack_on_sig_quit_(true),
       pruned_dalvik_cache_(false),
       // Initially assume we perceive jank in case the process state is never updated.