[Sync] Refactoring of sync integration test checkers to remove boilerplate await methods.

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

 // Copyright 2016 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 "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/sync/chrome_sync_client.h"
 #include "chrome/browser/sync/profile_sync_service_factory.h"
 #include "chrome/browser/sync/test/integration/profile_sync_service_harness.h"
@@ skipping 73 matching lines @@
 
   std::set<Observer*> observers_;
 };
 
 // A StatusChangeChecker for checking the status of keys in a
 // TestModelTypeService::Store.
 class KeyChecker : public StatusChangeChecker,
                    public TestModelTypeService::Observer {
  public:
   KeyChecker(TestModelTypeService* service, const std::string& key)
-      : service_(service), key_(key) {}
+      : service_(service), key_(key) {
+    service_->AddObserver(this);
+  }
+
+  ~KeyChecker() override { service_->RemoveObserver(this); }
 
   void OnApplySyncChanges() override { CheckExitCondition(); }
 
-  bool Wait() {
-    if (IsExitConditionSatisfied()) {
-      DVLOG(1) << "Wait() -> Exit before waiting: " << GetDebugMessage();
-      return true;
-    }
-
-    service_->AddObserver(this);
-    StartBlockingWait();
-    service_->RemoveObserver(this);
-    return !TimedOut();
-  }
-
  protected:
   TestModelTypeService* const service_;
   const std::string key_;
 };
 
 // Wait for data for a key to have a certain value.
 class DataChecker : public KeyChecker {
  public:
   DataChecker(TestModelTypeService* service,
               const std::string& key,
@@ skipping 212 matching lines @@
   model2->SetServiceError(syncer::SyncError::DATATYPE_ERROR);
   // Write an item on model 1 to trigger a GetUpdates in model 2.
   model1->WriteItem(kKey1, kValue2);
 
   // The type should stop syncing but keep tracking metadata.
   ASSERT_TRUE(PrefsNotRunningChecker(GetSyncService(1)).Wait());
   ASSERT_EQ(1U, model2->db().metadata_count());
   model2->WriteItem(kKey2, kValue2);
   ASSERT_EQ(2U, model2->db().metadata_count());
 }