Add All-Users project to store meta data for all users

This change adds a migration that creates an All-Users project for
storing meta data for all users. With this change no data is stored in
this repository yet, but future changes will e.g. store user
preferences in this repository by creating a ref per user.

Change-Id: Ib1ba5e4c2fb7a2f8e49d3bcf994c99d9e911475c
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-server/src/main/java/com/google/gerrit/server/project/ProjectCacheImpl.java

@@ -22,6 +22,7 @@ import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.server.cache.CacheModule;
 import com.google.gerrit.server.config.AllProjectsName;
+import com.google.gerrit.server.config.AllUsersName;
 import com.google.gerrit.server.git.GitRepositoryManager;
 import com.google.gerrit.server.git.ProjectConfig;
 import com.google.inject.Inject;
@@ -74,6 +75,7 @@ public class ProjectCacheImpl implements ProjectCache {
   }
 
   private final AllProjectsName allProjectsName;
+  private final AllUsersName allUsersName;
   private final LoadingCache<String, ProjectState> byName;
   private final LoadingCache<ListKey, SortedSet<Project.NameKey>> list;
   private final Lock listLock;
@@ -82,10 +84,12 @@ public class ProjectCacheImpl implements ProjectCache {
   @Inject
   ProjectCacheImpl(
       final AllProjectsName allProjectsName,
+      final AllUsersName allUsersName,
       @Named(CACHE_NAME) LoadingCache<String, ProjectState> byName,
       @Named(CACHE_LIST) LoadingCache<ListKey, SortedSet<Project.NameKey>> list,
       ProjectCacheClock clock) {
     this.allProjectsName = allProjectsName;
+    this.allUsersName = allUsersName;
     this.byName = byName;
     this.list = list;
     this.listLock = new ReentrantLock(true /* fair */);
@@ -103,6 +107,16 @@ public class ProjectCacheImpl implements ProjectCache {
     return state;
   }
 
+  @Override
+  public ProjectState getAllUsers() {
+    ProjectState state = get(allUsersName);
+    if (state == null) {
+      // This should never occur.
+      throw new IllegalStateException("Missing project " + allUsersName);
+    }
+    return state;
+  }
+
   @Override
   public ProjectState get(final Project.NameKey projectName) {
      try {