Remove legacy SESSIONS sync implementation

The SyncableService (SessionsSyncManager), the directory datatype
controller and all abstractions required for accomodating two
implementations are removed, together with the corresponding about flag
and feature toggle (kill switch).

Sync integration tests are updated because they also exercised the
legacy codepath.

[email protected],[email protected]

Bug: 895455
Change-Id: Ifaca1696e97f88b70b0c61ad89fed2372b239e46
Reviewed-on: https://chromium-review.googlesource.com/c/1340814
Reviewed-by: Mikel Astiz <[email protected]>
Reviewed-by: Marc Treib <[email protected]>
Commit-Queue: Mikel Astiz <[email protected]>
Cr-Commit-Position: refs/heads/master@{#609234}
diff --git a/components/sync_sessions/session_sync_service.cc b/components/sync_sessions/session_sync_service.cc
index a272fb7..54e7b8e 100644
--- a/components/sync_sessions/session_sync_service.cc
+++ b/components/sync_sessions/session_sync_service.cc
@@ -8,13 +8,10 @@
 
 #include "base/bind_helpers.h"
 #include "components/sync/base/report_unrecoverable_error.h"
-#include "components/sync/driver/sync_driver_switches.h"
 #include "components/sync/model_impl/client_tag_based_model_type_processor.h"
 #include "components/sync_sessions/favicon_cache.h"
-#include "components/sync_sessions/session_data_type_controller.h"
 #include "components/sync_sessions/session_sync_bridge.h"
 #include "components/sync_sessions/session_sync_prefs.h"
-#include "components/sync_sessions/sessions_sync_manager.h"
 #include "components/sync_sessions/sync_sessions_client.h"
 
 namespace sync_sessions {
@@ -24,35 +21,27 @@
     std::unique_ptr<SyncSessionsClient> sessions_client)
     : sessions_client_(std::move(sessions_client)) {
   DCHECK(sessions_client_);
-  if (base::FeatureList::IsEnabled(switches::kSyncUSSSessions)) {
-    sessions_sync_manager_ = std::make_unique<sync_sessions::SessionSyncBridge>(
-        base::BindRepeating(&SessionSyncService::NotifyForeignSessionUpdated,
-                            base::Unretained(this)),
-        sessions_client_.get(),
-        std::make_unique<syncer::ClientTagBasedModelTypeProcessor>(
-            syncer::SESSIONS,
-            base::BindRepeating(&syncer::ReportUnrecoverableError, channel)));
-  } else {
-    sessions_sync_manager_ =
-        std::make_unique<sync_sessions::SessionsSyncManager>(
-            base::BindRepeating(
-                &SessionSyncService::NotifyForeignSessionUpdated,
-                base::Unretained(this)),
-            sessions_client_.get());
-  }
+
+  bridge_ = std::make_unique<sync_sessions::SessionSyncBridge>(
+      base::BindRepeating(&SessionSyncService::NotifyForeignSessionUpdated,
+                          base::Unretained(this)),
+      sessions_client_.get(),
+      std::make_unique<syncer::ClientTagBasedModelTypeProcessor>(
+          syncer::SESSIONS,
+          base::BindRepeating(&syncer::ReportUnrecoverableError, channel)));
 }
 
 SessionSyncService::~SessionSyncService() {}
 
 syncer::GlobalIdMapper* SessionSyncService::GetGlobalIdMapper() const {
-  return sessions_sync_manager_->GetGlobalIdMapper();
+  return bridge_->GetGlobalIdMapper();
 }
 
 OpenTabsUIDelegate* SessionSyncService::GetOpenTabsUIDelegate() {
   if (!proxy_tabs_running_) {
     return nullptr;
   }
-  return sessions_sync_manager_->GetOpenTabsUIDelegate();
+  return bridge_->GetOpenTabsUIDelegate();
 }
 
 std::unique_ptr<base::CallbackList<void()>::Subscription>
@@ -62,22 +51,16 @@
 }
 
 void SessionSyncService::ScheduleGarbageCollection() {
-  sessions_sync_manager_->ScheduleGarbageCollection();
-}
-
-syncer::SyncableService* SessionSyncService::GetSyncableService() {
-  return sessions_sync_manager_->GetSyncableService();
+  bridge_->ScheduleGarbageCollection();
 }
 
 base::WeakPtr<syncer::ModelTypeControllerDelegate>
 SessionSyncService::GetControllerDelegate() {
-  return sessions_sync_manager_->GetModelTypeSyncBridge()
-      ->change_processor()
-      ->GetControllerDelegate();
+  return bridge_->change_processor()->GetControllerDelegate();
 }
 
 FaviconCache* SessionSyncService::GetFaviconCache() {
-  return sessions_sync_manager_->GetFaviconCache();
+  return bridge_->GetFaviconCache();
 }
 
 void SessionSyncService::ProxyTabsStateChanged(
@@ -95,7 +78,7 @@
 
 OpenTabsUIDelegate*
 SessionSyncService::GetUnderlyingOpenTabsUIDelegateForTest() {
-  return sessions_sync_manager_->GetOpenTabsUIDelegate();
+  return bridge_->GetOpenTabsUIDelegate();
 }
 
 void SessionSyncService::NotifyForeignSessionUpdated() {