Send UMA recording state to TranslateRanker.

ios/chrome/browser/translate/translate_ranker_metrics_provider.h

 // Copyright 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.
 
 #ifndef IOS_CHROME_BROWSER_TRANSLATE_TRANSLATE_RANKER_METRICS_PROVIDER_H_
 #define IOS_CHROME_BROWSER_TRANSLATE_TRANSLATE_RANKER_METRICS_PROVIDER_H_
 
 #include "components/metrics/metrics_provider.h"
 
 namespace translate {
 
 // Provides metrics related to the translate ranker.
 class TranslateRankerMetricsProvider : public metrics::MetricsProvider {
  public:
-  TranslateRankerMetricsProvider() {}
+  TranslateRankerMetricsProvider() : logging_enabled_(false) {}
   ~TranslateRankerMetricsProvider() override {}
 
- private:
   // From metrics::MetricsProvider...
   void ProvideGeneralMetrics(
       metrics::ChromeUserMetricsExtension* uma_proto) override;
+  void OnRecordingEnabled() override;
+  void OnRecordingDisabled() override;
+
+ private:
+  // Updates the logging state of all ranker instances.
+  void UpdateLoggingState();
+
+  // The current state of logging.
+  bool logging_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(TranslateRankerMetricsProvider);
 };
 
 }  // namespace translate
 
 #endif  // IOS_CHROME_BROWSER_TRANSLATE_TRANSLATE_RANKER_METRICS_PROVIDER_H_