Remove PermissionBackend.*#user()

This commit removes the user() method from all PermissionBackend
subclasses. This method just encourages callers to pass around a
PermissionBackend when they really want to pass around a CurrentUser
and/or ChangeNotes.

Passing around heavy objects that represent a subsystem for the benefit
of getting smaller objects from it is an anti-pattern. We had this issue
at a larger scale with {Ref,Project,Change}Control that were often just
passed around to have a user and/or entity information. Removing the
user() methods should prevent that.

This refactoring also uncovered some wrongdoing that we already had in
the code as a direct result from passing PermissionBackends around (see
previous commit).

Removing user() comes at the (small) const that every PermissionBackend
has to implement #testCond by itsself, which seems fair and like a
better pattern in general.

Change-Id: Ibae1fc25e51228dca2acaf0faec76beee539da01

java/com/google/gerrit/server/permissions/DefaultPermissionBackend.java

@@ -23,6 +23,7 @@ import com.google.gerrit.common.data.PermissionRule;
 import com.google.gerrit.common.data.PermissionRule.Action;
 import com.google.gerrit.extensions.api.access.GlobalOrPluginPermission;
 import com.google.gerrit.extensions.api.access.PluginPermission;
+import com.google.gerrit.extensions.conditions.BooleanCondition;
 import com.google.gerrit.extensions.restapi.AuthException;
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.AccountGroup;
@@ -32,6 +33,7 @@ import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.PeerDaemonUser;
 import com.google.gerrit.server.account.CapabilityCollection;
 import com.google.gerrit.server.cache.PerThreadCache;
+import com.google.gerrit.server.permissions.PermissionBackendCondition.WithUser;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.gerrit.server.project.ProjectState;
 import com.google.inject.Inject;
@@ -97,11 +99,6 @@ public class DefaultPermissionBackend extends PermissionBackend {
       this.user = checkNotNull(user, "user");
     }
 
-    @Override
-    public CurrentUser user() {
-      return user;
-    }
-
     @Override
     public ForProject project(Project.NameKey project) {
       try {
@@ -138,6 +135,11 @@ public class DefaultPermissionBackend extends PermissionBackend {
       return ok;
     }
 
+    @Override
+    public BooleanCondition testCond(GlobalOrPluginPermission perm) {
+      return new PermissionBackendCondition.WithUser(this, perm, user);
+    }
+
     private boolean can(GlobalOrPluginPermission perm) throws PermissionBackendException {
       if (perm instanceof GlobalPermission) {
         return can((GlobalPermission) perm);