Replace use of AccountGroup by an interface for various classes

Previously, GroupDescription.Internal served only as a marker for
internal groups and simply delegated to AccountGroup. By converting
GroupDescription.Internal to a real interface, we gain a lot of
flexibility. For instance, we are free to use another class to
represent internal groups (which will be necessary for the migration
of groups to NoteDb).

Change-Id: If7397898d8508184a2ccdc7c371ed60ada7d6f3e

gerrit-common/src/main/java/com/google/gerrit/common/data/GroupDescription.java

@@ -16,6 +16,7 @@ package com.google.gerrit.common.data;
 
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.reviewdb.client.AccountGroup;
+import java.sql.Timestamp;
 
 /** Group methods exposed by the GroupBackend. */
 public class GroupDescription {
@@ -42,10 +43,18 @@ public class GroupDescription {
     String getUrl();
   }
 
-  /** The extended information exposed by internal groups backed by an AccountGroup. */
+  /** The extended information exposed by internal groups. */
   public interface Internal extends Basic {
-    /** @return the backing AccountGroup. */
-    AccountGroup getAccountGroup();
+
+    AccountGroup.Id getId();
+
+    String getDescription();
+
+    AccountGroup.UUID getOwnerGroupUUID();
+
+    boolean isVisibleToAll();
+
+    Timestamp getCreatedOn();
   }
 
   private GroupDescription() {}

gerrit-common/src/main/java/com/google/gerrit/common/data/GroupDescriptions.java

@@ -17,18 +17,11 @@ package com.google.gerrit.common.data;
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.common.PageLinks;
 import com.google.gerrit.reviewdb.client.AccountGroup;
+import java.sql.Timestamp;
 
 /** Utility class for building GroupDescription objects. */
 public class GroupDescriptions {
 
-  @Nullable
-  public static AccountGroup toAccountGroup(GroupDescription.Basic group) {
-    if (group instanceof GroupDescription.Internal) {
-      return ((GroupDescription.Internal) group).getAccountGroup();
-    }
-    return null;
-  }
-
   public static GroupDescription.Internal forAccountGroup(AccountGroup group) {
     return new GroupDescription.Internal() {
       @Override
@@ -41,11 +34,6 @@ public class GroupDescriptions {
         return group.getName();
       }
 
-      @Override
-      public AccountGroup getAccountGroup() {
-        return group;
-      }
-
       @Override
       @Nullable
       public String getEmailAddress() {
@@ -53,10 +41,34 @@ public class GroupDescriptions {
       }
 
       @Override
-      @Nullable
       public String getUrl() {
         return "#" + PageLinks.toGroup(getGroupUUID());
       }
+
+      @Override
+      public AccountGroup.Id getId() {
+        return group.getId();
+      }
+
+      @Override
+      public String getDescription() {
+        return group.getDescription();
+      }
+
+      @Override
+      public AccountGroup.UUID getOwnerGroupUUID() {
+        return group.getOwnerGroupUUID();
+      }
+
+      @Override
+      public boolean isVisibleToAll() {
+        return group.isVisibleToAll();
+      }
+
+      @Override
+      public Timestamp getCreatedOn() {
+        return group.getCreatedOn();
+      }
     };
   }
 

gerrit-common/src/main/java/com/google/gerrit/common/data/GroupInfo.java

@@ -46,8 +46,7 @@ public class GroupInfo {
     url = a.getUrl();
 
     if (a instanceof GroupDescription.Internal) {
-      AccountGroup group = ((GroupDescription.Internal) a).getAccountGroup();
-      description = group.getDescription();
+      description = ((GroupDescription.Internal) a).getDescription();
     }
   }