Fix MetricsServiceClients to use SyncDisableObservers state.

ios/chrome/browser/metrics/ios_chrome_metrics_service_client.h

 // 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.
 
 #ifndef IOS_CHROME_BROWSER_METRICS_IOS_CHROME_METRICS_SERVICE_CLIENT_H_
 #define IOS_CHROME_BROWSER_METRICS_IOS_CHROME_METRICS_SERVICE_CLIENT_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 59 matching lines @@
   void InitializeSystemProfileMetrics(
       const base::Closure& done_callback) override;
   void CollectFinalMetricsForLog(const base::Closure& done_callback) override;
   std::unique_ptr<metrics::MetricsLogUploader> CreateUploader(
       const std::string& server_url,
       const std::string& mime_type,
       const base::Callback<void(int)>& on_upload_complete) override;
   base::TimeDelta GetStandardUploadInterval() override;
   base::string16 GetRegistryBackupKey() override;
   void OnRendererProcessCrash() override;
+  bool IsHistorySyncEnabledOnAllProfiles() override;
 
   // ukm::HistoryDeleteObserver:
   void OnHistoryDeleted() override;
 
   // ukm::SyncDisableObserver:
   void OnSyncPrefsChanged(bool must_purge) override;
 
   // web::GlobalWebStateObserver:
   void WebStateDidStartLoading(web::WebState* web_state) override;
   void WebStateDidStopLoading(web::WebState* web_state) override;
@@ skipping 86 matching lines @@
   // Whether this client has already uploaded profiler data during this session.
   // Profiler data is uploaded at most once per session.
   bool has_uploaded_profiler_data_;
 
   base::WeakPtrFactory<IOSChromeMetricsServiceClient> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(IOSChromeMetricsServiceClient);
 };
 
 #endif  // IOS_CHROME_BROWSER_METRICS_IOS_CHROME_METRICS_SERVICE_CLIENT_H_