ActivityThread: Only update code paths that have been added

When an ApplicationInfo object is updated and we want to update
code paths without restarting the app's process, we need to make
sure that we only update the paths that have changed. This means
diffing between the old paths and the new paths.

Test: watch /proc/<pid>/maps for dex entries before and after
      running adb exec-out am update-appinfos all <package>
Change-Id: I6855d860478ade3184bbb578a5483d8548396daa