[sync] WebContentsObserver based sessions notifications

ios/chrome/browser/sync/ios_chrome_sync_client.mm

 // Copyright 2015 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.
 
 #include "ios/chrome/browser/sync/ios_chrome_sync_client.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 99 matching lines @@
     }
     return url.is_valid() && !url.SchemeIs(kChromeUIScheme) &&
            !url.SchemeIsFile();
   }
 
   sync_sessions::SyncedWindowDelegatesGetter* GetSyncedWindowDelegatesGetter()
       override {
     return window_delegates_getter_.get();
   }
 
-  std::unique_ptr<sync_sessions::LocalSessionEventRouter>
-  GetLocalSessionEventRouter() override {
+  sync_sessions::LocalSessionEventRouter* GetLocalSessionEventRouter()
+      override {
     syncer::SyncableService::StartSyncFlare flare(
         ios::sync_start_util::GetFlareForSyncableService(
             browser_state_->GetStatePath()));
-    return base::MakeUnique<IOSChromeLocalSessionEventRouter>(browser_state_,
-                                                              this, flare);
+    local_session_event_router_ =
+        base::MakeUnique<IOSChromeLocalSessionEventRouter>(browser_state_, this,
+                                                           flare);
+    return local_session_event_router_.get();
   }
 
  private:
   ios::ChromeBrowserState* const browser_state_;
   const std::unique_ptr<sync_sessions::SyncedWindowDelegatesGetter>
       window_delegates_getter_;
+  std::unique_ptr<IOSChromeLocalSessionEventRouter> local_session_event_router_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncSessionsClientImpl);
 };
 
 }  // namespace
 
 IOSChromeSyncClient::IOSChromeSyncClient(ios::ChromeBrowserState* browser_state)
     : browser_state_(browser_state),
       sync_sessions_client_(
           base::MakeUnique<SyncSessionsClientImpl>(browser_state)),
@@ skipping 282 matching lines @@
         IOSChromeProfileSyncServiceFactory::GetForBrowserState(browser_state);
     if (profile_sync_service != nullptr) {
       const syncer::DeviceInfoTracker* tracker =
           profile_sync_service->GetDeviceInfoTracker();
       if (tracker != nullptr) {
         trackers->push_back(tracker);
       }
     }
   }
 }