Fix "unused variable" warnings.

chrome/browser/interstitials/chrome_metrics_helper.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 CHROME_BROWSER_INTERSTITIALS_CHROME_METRICS_HELPER_H_
 #define CHROME_BROWSER_INTERSTITIALS_CHROME_METRICS_HELPER_H_
 
 #include <string>
 
 #include "base/macros.h"
@@ skipping 28 matching lines @@
 
  protected:
   // security_interstitials::MetricsHelper methods:
   void RecordExtraUserDecisionMetrics(
       security_interstitials::MetricsHelper::Decision decision) override;
   void RecordExtraUserInteractionMetrics(
       security_interstitials::MetricsHelper::Interaction interaction) override;
   void RecordExtraShutdownMetrics() override;
 
  private:
+#if defined(ENABLE_CAPTIVE_PORTAL_DETECTION) || defined(ENABLE_EXTENSIONS)
   content::WebContents* web_contents_;
+#endif
   const GURL request_url_;
   const std::string sampling_event_name_;
 #if defined(ENABLE_EXTENSIONS)
   std::unique_ptr<extensions::ExperienceSamplingEvent> sampling_event_;
 #endif
 #if defined(ENABLE_CAPTIVE_PORTAL_DETECTION)
   std::unique_ptr<CaptivePortalMetricsRecorder> captive_portal_recorder_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(ChromeMetricsHelper);
 };
 
 #endif  // CHROME_BROWSER_INTERSTITIALS_CHROME_METRICS_HELPER_H_