InlineEdit: Add container to represent change edit

Change edits are created on top of patch sets and are virtual patch
sets that don't exist in the database. A max of one edit per user per
change is stored on ref:

  refs/users/UU/UUUU/edit-CCCC

for edit by user UUUU on top of patch set P of CCCC, where user account
is sharded in the same way as for refs/changes.  The parent of the edit
is SHA-1 of the patch set P it is based on.

Change-Id: I736f5b954ec539a453cf0500a7bd97547bb494d7

gerrit-server/src/main/java/com/google/gerrit/server/edit/ChangeEdit.java

@@ -0,0 +1,69 @@
+// Copyright (C) 2014 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.edit;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.RefNames;
+import com.google.gerrit.reviewdb.client.RevId;
+import com.google.gerrit.server.IdentifiedUser;
+
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.Ref;
+
+/**
+ * A single user's edit for a change.
+ * <p>
+ * There is max. one edit per user per change. Edits are stored on refs:
+ * refs/users/UU/UUUU/edit-CCCC where UU/UUUU is sharded representation
+ * of user account and CCCC is change number.
+ */
+public class ChangeEdit {
+  private final IdentifiedUser user;
+  private final Change change;
+  private final Ref ref;
+
+  public ChangeEdit(IdentifiedUser user, Change change, Ref ref) {
+    checkNotNull(user);
+    checkNotNull(change);
+    checkNotNull(ref);
+    this.user = user;
+    this.change = change;
+    this.ref = ref;
+  }
+
+  public Change getChange() {
+    return change;
+  }
+
+  public IdentifiedUser getUser() {
+    return user;
+  }
+
+  public Ref getRef() {
+    return ref;
+  }
+
+  public RevId getRevision() {
+    return new RevId(ObjectId.toString(ref.getObjectId()));
+  }
+
+  public String getRefName() {
+    return String.format("%s/edit-%d",
+        RefNames.refsUsers(user.getAccountId()),
+        change.getId().get());
+  }
+}