Add init step for enabling experimental features

This is intended for features that are experimental enough that we want
to hide them behind some warning text, but not so experimental that we
want them to be enabled only with obscure or undocumented commands.

The two current features, to nobody's surprise, are NoteDb and
PolyGerrit.

Enabling NoteDb sets all NotesMigration options to enabled, in
particular disabling ReviewDb for changes, although the tables are
still created since they're still in the schema.

For PolyGerrit, the main question is what the default UI is, as PG has
been part of the WAR for a while now. It is also possible to disable
the GWT UI, although this is not the suggested default option since
there are still some missing features that make switching back
worthwhile.

Change-Id: I419d73eb5944b7c4c8651b86c6efd25a969e60b5

gerrit-server/src/main/java/com/google/gerrit/server/notedb/ConfigNotesMigration.java

@@ -44,7 +44,7 @@ public class ConfigNotesMigration extends NotesMigration {
     }
   }
 
-  private static final String NOTE_DB = "noteDb";
+  public static final String SECTION_NOTE_DB = "noteDb";
 
   // All of these names must be reflected in the allowed set in checkConfig.
   private static final String DISABLE_REVIEW_DB = "disableReviewDb";
@@ -62,9 +62,9 @@ public class ConfigNotesMigration extends NotesMigration {
             READ.toLowerCase(),
             WRITE.toLowerCase(),
             SEQUENCE.toLowerCase());
-    for (String t : cfg.getSubsections(NOTE_DB)) {
+    for (String t : cfg.getSubsections(SECTION_NOTE_DB)) {
       checkArgument(keys.contains(t.toLowerCase()), "invalid NoteDb table: %s", t);
-      for (String key : cfg.getNames(NOTE_DB, t)) {
+      for (String key : cfg.getNames(SECTION_NOTE_DB, t)) {
         checkArgument(allowed.contains(key.toLowerCase()), "invalid NoteDb key: %s.%s", t, key);
       }
     }
@@ -72,8 +72,11 @@ public class ConfigNotesMigration extends NotesMigration {
 
   public static Config allEnabledConfig() {
     Config cfg = new Config();
-    cfg.setBoolean(NOTE_DB, CHANGES.key(), WRITE, true);
-    cfg.setBoolean(NOTE_DB, CHANGES.key(), READ, true);
+    cfg.setBoolean(SECTION_NOTE_DB, CHANGES.key(), WRITE, true);
+    cfg.setBoolean(SECTION_NOTE_DB, CHANGES.key(), READ, true);
+    cfg.setBoolean(SECTION_NOTE_DB, CHANGES.key(), SEQUENCE, true);
+    cfg.setString(SECTION_NOTE_DB, CHANGES.key(), PRIMARY_STORAGE, PrimaryStorage.NOTE_DB.name());
+    cfg.setBoolean(SECTION_NOTE_DB, CHANGES.key(), DISABLE_REVIEW_DB, true);
     return cfg;
   }
 
@@ -87,18 +90,19 @@ public class ConfigNotesMigration extends NotesMigration {
   public ConfigNotesMigration(@GerritServerConfig Config cfg) {
     checkConfig(cfg);
 
-    writeChanges = cfg.getBoolean(NOTE_DB, CHANGES.key(), WRITE, false);
-    readChanges = cfg.getBoolean(NOTE_DB, CHANGES.key(), READ, false);
+    writeChanges = cfg.getBoolean(SECTION_NOTE_DB, CHANGES.key(), WRITE, false);
+    readChanges = cfg.getBoolean(SECTION_NOTE_DB, CHANGES.key(), READ, false);
 
     // Reading change sequence numbers from NoteDb is not the default even if
     // reading changes themselves is. Once this is enabled, it's not easy to
     // undo: ReviewDb might hand out numbers that have already been assigned by
     // NoteDb. This decision for the default may be reevaluated later.
-    readChangeSequence = cfg.getBoolean(NOTE_DB, CHANGES.key(), SEQUENCE, false);
+    readChangeSequence = cfg.getBoolean(SECTION_NOTE_DB, CHANGES.key(), SEQUENCE, false);
 
     changePrimaryStorage =
-        cfg.getEnum(NOTE_DB, CHANGES.key(), PRIMARY_STORAGE, PrimaryStorage.REVIEW_DB);
-    disableChangeReviewDb = cfg.getBoolean(NOTE_DB, CHANGES.key(), DISABLE_REVIEW_DB, false);
+        cfg.getEnum(SECTION_NOTE_DB, CHANGES.key(), PRIMARY_STORAGE, PrimaryStorage.REVIEW_DB);
+    disableChangeReviewDb =
+        cfg.getBoolean(SECTION_NOTE_DB, CHANGES.key(), DISABLE_REVIEW_DB, false);
 
     checkArgument(
         !(disableChangeReviewDb && changePrimaryStorage != PrimaryStorage.NOTE_DB),

gerrit-server/src/main/java/com/google/gerrit/server/notedb/NoteDbTable.java

@@ -14,11 +14,11 @@
 
 package com.google.gerrit.server.notedb;
 
-enum NoteDbTable {
+public enum NoteDbTable {
   ACCOUNTS,
   CHANGES;
 
-  String key() {
+  public String key() {
     return name().toLowerCase();
   }
 

gerrit-server/src/main/java/com/google/gerrit/server/schema/SchemaUpdater.java

@@ -50,7 +50,10 @@ public class SchemaUpdater {
 
   @Inject
   SchemaUpdater(
-      SchemaFactory<ReviewDb> schema, SitePaths site, SchemaCreator creator, Injector parent) {
+      @ReviewDbFactory SchemaFactory<ReviewDb> schema,
+      SitePaths site,
+      SchemaCreator creator,
+      Injector parent) {
     this.schema = schema;
     this.site = site;
     this.creator = creator;