Restored an option to enable enhanced bookmarks experiment from Finch

chrome/browser/bookmarks/enhanced_bookmarks_features.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_BOOKMARKS_ENHANCED_BOOKMARKS_FEATURES_H_
 #define CHROME_BROWSER_BOOKMARKS_ENHANCED_BOOKMARKS_FEATURES_H_
 
 #include <string>
 
 #include "extensions/common/extension.h"
 
 class PrefService;
 
+// States for bookmark experiment. They are set by Chrome sync into
+// sync_driver::prefs::kEnhancedBookmarksExperimentEnabled user preference and
+// used for UMA reporting as well.
 enum BookmarksExperimentState {
   kNoBookmarksExperiment,
   kBookmarksExperimentEnabled,
-  kBookmarksExperimentEnabledUserOptOut
+  kBookmarksExperimentEnabledUserOptOut,
+  kBookmarksExperimentEnabledFromFinch,
+  kBookmarksExperimentOptOutFromFinch,
+  kBookmarksExperimentEnabledFromFinchUserSignedIn,
+  kBookmarksExperimentEnumSize
 };
 
+// Returns true and sets |extension_id| if bookmarks experiment enabled
+//         false if no bookmark experiment or extension id is empty.
+bool GetBookmarksExperimentExtensionID(const PrefService* user_prefs,
+                                       std::string* extension_id);
+
+// Updates bookmark experiment state based on information from Chrome sync
+// and Finch experiments.
+void UpdateBookmarksExperimentState(const PrefService* user_prefs,
+                                    PrefService* local_state,
+                                    bool user_signed_in);
+
 // Sets flag to opt-in user into Finch experiment.
-void UpdateBookmarksExperiment(
+void ForceFinchBookmarkExperimentIfNeeded(
     PrefService* local_state,
     BookmarksExperimentState bookmarks_experiment_state);
 
 // Returns true if enhanced bookmarks experiment is enabled.
+// Experiment could be enable from Chrome sync or from Finch.
 bool IsEnhancedBookmarksExperimentEnabled();
 
 // Returns true when flag enable-dom-distiller is set or enabled from Finch.
 bool IsEnableDomDistillerSet();
 
 // Returns true when flag enable-sync-articles is set or enabled from Finch.
 bool IsEnableSyncArticlesSet();
 
-// Get extension id from Finch EnhancedBookmarks group parameters.
-std::string GetEnhancedBookmarksExtensionIdFromFinch();
-
 #endif  // CHROME_BROWSER_BOOKMARKS_ENHANCED_BOOKMARKS_FEATURES_H_