ChangeUtil: Fix findChanges for anonymous users

In I7710befa I didn't realize the user provider was a
Provider<IdentifiedUser>, which caused a ProvisionException when
anonymous users tried to use the REST API to look up changes by
something other than a number. This wasn't noticed sooner because it
didn't affect the web UI, which exclusively uses change numbers.

Change to Provider<CurrentUser> and use asIdentifiedUser only at the
sites where an IdentifiedUser is needed. This will throw a different
unchecked exception type on failure (UnsupportedOperationException
instead of ProvisionException), but callers aren't depending on that.

Add a test, during which I also discovered a bug in the implementation
of AbstractDaemonTest#setApiUserAnonymous. That wasn't already causing
failures because the only user was using it to avoid some side effects
that "may" have happened.

Change-Id: Idbad114d6f5a61167d6fda32ee0093558491cf8e

gerrit-server/src/main/java/com/google/gerrit/server/ChangeUtil.java

@@ -177,7 +177,7 @@ public class ChangeUtil {
     return subject;
   }
 
-  private final Provider<IdentifiedUser> user;
+  private final Provider<CurrentUser> user;
   private final Provider<ReviewDb> db;
   private final Provider<InternalChangeQuery> queryProvider;
   private final ChangeControl.GenericFactory changeControlFactory;
@@ -192,7 +192,7 @@ public class ChangeUtil {
   private final StarredChangesUtil starredChangesUtil;
 
   @Inject
-  ChangeUtil(Provider<IdentifiedUser> user,
+  ChangeUtil(Provider<CurrentUser> user,
       Provider<ReviewDb> db,
       Provider<InternalChangeQuery> queryProvider,
       ChangeControl.GenericFactory changeControlFactory,
@@ -238,7 +238,7 @@ public class ChangeUtil {
       RevCommit commitToRevert =
           revWalk.parseCommit(ObjectId.fromString(patch.getRevision().get()));
 
-      PersonIdent authorIdent = user.get()
+      PersonIdent authorIdent = user.get().asIdentifiedUser()
           .newCommitterIdent(myIdent.getWhen(), myIdent.getTimeZone());
 
       if (commitToRevert.getParentCount() == 0) {