reland of [sync] Add Sessions integration tests

chrome/browser/sync/test/integration/session_hierarchy_match_checker.cc

+// Copyright (c) 2017 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/sync/test/integration/session_hierarchy_match_checker.h"
+
+SessionHierarchyMatchChecker::SessionHierarchyMatchChecker(
+    const fake_server::SessionsHierarchy& sessions_hierarchy,
+    browser_sync::ProfileSyncService* service,
+    fake_server::FakeServer* fake_server)
+    : SingleClientStatusChangeChecker(service),
+      sessions_hierarchy_(sessions_hierarchy),
+      verifier_(fake_server) {}
+
+bool SessionHierarchyMatchChecker::IsExitConditionSatisfied() {
+  return verifier_.VerifySessions(sessions_hierarchy_);
+}
+
+std::string SessionHierarchyMatchChecker::GetDebugMessage() const {
+  return "Waiting for matching sessions hierarchy to be reflected in fake "
+         "server";
+}