Add callback for notifying that startup is completed

Add a callback that can be called to denote that application startup
is completed. This may affect how the profile is collected and how
startup related caches are managed.

Bug: 123377072
Bug: 120671223
Test: test-art-host
Change-Id: If7eb8909cc5e99082a2243b5029380244b46174d
diff --git a/test/1002-notify-startup/info.txt b/test/1002-notify-startup/info.txt
new file mode 100644
index 0000000..1ebca87
--- /dev/null
+++ b/test/1002-notify-startup/info.txt
@@ -0,0 +1 @@
+Test that the startup completed callback works.