[sync] WebContentsObserver based sessions notifications

chrome/browser/ui/sync/tab_contents_synced_tab_delegate.cc

 // Copyright (c) 2012 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 "chrome/browser/ui/sync/tab_contents_synced_tab_delegate.h"
 
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/sessions/session_tab_helper.h"
+#include "chrome/browser/sync/sessions/sync_sessions_router_tab_helper.h"
 #include "chrome/common/features.h"
 #include "components/sessions/content/content_serialized_navigation_builder.h"
 #include "components/sync_sessions/sync_sessions_client.h"
 #include "components/sync_sessions/synced_window_delegate.h"
 #include "components/sync_sessions/synced_window_delegates_getter.h"
 #include "content/public/browser/favicon_status.h"
 #include "content/public/browser/navigation_controller.h"
 #include "content/public/browser/navigation_entry.h"
 #include "content/public/browser/web_contents.h"
 #include "extensions/features/features.h"
@@ skipping 137 matching lines @@
   for (int i = 0; i < entry_count; ++i) {
     const GURL& virtual_url = GetVirtualURLAtIndex(i);
     if (!virtual_url.is_valid())
       continue;
 
     if (sessions_client->ShouldSyncURL(virtual_url))
       return true;
   }
   return false;
 }
+
+SessionID::id_type TabContentsSyncedTabDelegate::GetSourceTabID() const {
+  sync_sessions::SyncSessionsRouterTabHelper* helper =
+      sync_sessions::SyncSessionsRouterTabHelper::FromWebContents(
+          web_contents_);
+  return helper->source_tab_id();
+}