LoadedApk: Notify cross-package use only when code is requested.

Cross-package use is quite common when only resources are being
considered. A common example is that any application that declares
itself <searchable /> will see cross package resource only use from
the system_server.

Test: manual instrumentation.
Change-Id: Ic7ad166c71a23c6026f4e12bb52309a50210aaaf