Merge changes I2b470424,I8b45988a,Ib1f79cf4 into stable-3.3

* changes:
  Ship a list of default experiments from the backend and allow disabling
  Revert "Clean up comment experiment flags"
  Make UI experiments configurable from gerrit.config

java/com/google/gerrit/httpd/raw/IndexHtmlUtil.java

@@ -20,6 +20,7 @@ import static java.util.stream.Collectors.toSet;
 
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.common.UsedAt;
@@ -37,15 +38,21 @@ import java.net.URISyntaxException;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
+import org.eclipse.jgit.lib.Config;
 
 /** Helper for generating parts of {@code index.html}. */
 @UsedAt(Project.GOOGLE)
 public class IndexHtmlUtil {
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();
 
+  static final ImmutableSet<String> DEFAULT_EXPERIMENTS =
+      ImmutableSet.of(
+          "UiFeature__patchset_comments", "UiFeature__patchset_choice_for_comment_links");
+
   private static final Gson GSON = OutputFormat.JSON_COMPACT.newGson();
   /**
    * Returns both static and dynamic parameters of {@code index.html}. The result is to be used when
@@ -53,6 +60,7 @@ public class IndexHtmlUtil {
    */
   public static ImmutableMap<String, Object> templateData(
       GerritApi gerritApi,
+      Config gerritServerConfig,
       String canonicalURL,
       String cdnPath,
       String faviconPath,
@@ -66,7 +74,13 @@ public class IndexHtmlUtil {
                 canonicalURL, cdnPath, faviconPath, urlParameterMap, urlInScriptTagOrdainer))
         .putAll(dynamicTemplateData(gerritApi, requestedURL));
 
-    Set<String> enabledExperiments = experimentData(urlParameterMap);
+    Set<String> enabledExperiments = new HashSet<>();
+    Arrays.stream(gerritServerConfig.getStringList("experiments", null, "enabled"))
+        .forEach(enabledExperiments::add);
+    DEFAULT_EXPERIMENTS.forEach(enabledExperiments::add);
+    Arrays.stream(gerritServerConfig.getStringList("experiments", null, "disabled"))
+        .forEach(enabledExperiments::remove);
+    experimentData(urlParameterMap).forEach(enabledExperiments::add);
     if (!enabledExperiments.isEmpty()) {
       data.put("enabledExperiments", serializeObject(GSON, enabledExperiments).toString());
     }

java/com/google/gerrit/httpd/raw/IndexServlet.java

@@ -34,6 +34,7 @@ import java.util.function.Function;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
+import org.eclipse.jgit.lib.Config;
 
 public class IndexServlet extends HttpServlet {
   private static final long serialVersionUID = 1L;
@@ -42,6 +43,7 @@ public class IndexServlet extends HttpServlet {
   @Nullable private final String cdnPath;
   @Nullable private final String faviconPath;
   private final GerritApi gerritApi;
+  private final Config gerritServerConfig;
   private final SoySauce soySauce;
   private final Function<String, SanitizedContent> urlOrdainer;
 
@@ -49,11 +51,13 @@ public class IndexServlet extends HttpServlet {
       @Nullable String canonicalUrl,
       @Nullable String cdnPath,
       @Nullable String faviconPath,
-      GerritApi gerritApi) {
+      GerritApi gerritApi,
+      Config gerritServerConfig) {
     this.canonicalUrl = canonicalUrl;
     this.cdnPath = cdnPath;
     this.faviconPath = faviconPath;
     this.gerritApi = gerritApi;
+    this.gerritServerConfig = gerritServerConfig;
     this.soySauce =
         SoyFileSet.builder()
             .add(Resources.getResource("com/google/gerrit/httpd/raw/PolyGerritIndexHtml.soy"))
@@ -74,7 +78,14 @@ public class IndexServlet extends HttpServlet {
       // TODO(hiesel): Remove URL ordainer as parameter once Soy is consistent
       ImmutableMap<String, Object> templateData =
           IndexHtmlUtil.templateData(
-              gerritApi, canonicalUrl, cdnPath, faviconPath, parameterMap, urlOrdainer, requestUrl);
+              gerritApi,
+              gerritServerConfig,
+              canonicalUrl,
+              cdnPath,
+              faviconPath,
+              parameterMap,
+              urlOrdainer,
+              requestUrl);
       renderer = soySauce.renderTemplate("com.google.gerrit.httpd.raw.Index").setData(templateData);
     } catch (URISyntaxException | RestApiException e) {
       throw new IOException(e);

java/com/google/gerrit/httpd/raw/StaticModule.java

@@ -225,7 +225,7 @@ public class StaticModule extends ServletModule {
       String cdnPath =
           options.useDevCdn() ? options.devCdn() : cfg.getString("gerrit", null, "cdnPath");
       String faviconPath = cfg.getString("gerrit", null, "faviconPath");
-      return new IndexServlet(canonicalUrl, cdnPath, faviconPath, gerritApi);
+      return new IndexServlet(canonicalUrl, cdnPath, faviconPath, gerritApi, cfg);
     }
 
     @Provides