Recovers on boot when scan of data app fails

Prior to this change, system apps that had updated versions installed
that could not be scanned on boot, did not have a fallback mechanism to
restore the system app. With this change, we prepare for such a scenario
and restore the system app using the existing "expecting better"
mechanism.

Test: manual; muck with an APK in /data/app and reboot.
Bug: 117471712
Change-Id: Ic50880cc04e92003c2a20869cf38835af7ce3ccb

services/core/java/com/android/server/pm/PackageManagerService.java

@@ -2684,6 +2684,11 @@ public class PackageManagerService extends IPackageManager.Stub
                         if (disabledPs.codePath == null || !disabledPs.codePath.exists()
                                 || disabledPs.pkg == null) {
                             possiblyDeletedUpdatedSystemApps.add(ps.name);
+                        } else {
+                            // We're expecting that the system app should remain disabled, but add
+                            // it to expecting better to recover in case the data version cannot
+                            // be scanned.
+                            mExpectingBetter.put(disabledPs.name, disabledPs.codePath);
                         }
                     }
                 }