Make `chrome` target build without unused data members on Linux.

chrome/browser/metrics/chrome_metrics_service_client.cc

 // Copyright 2014 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/metrics/chrome_metrics_service_client.h"
 
 #include <stddef.h>
 
 #include <vector>
 
@@ skipping 115 matching lines @@
   return false;
 #endif
 }
 
 }  // namespace
 
 
 ChromeMetricsServiceClient::ChromeMetricsServiceClient(
     metrics::MetricsStateManager* state_manager)
     : metrics_state_manager_(state_manager),
+#if defined(OS_CHROMEOS)
       chromeos_metrics_provider_(nullptr),
+#endif
       waiting_for_collect_final_metrics_step_(false),
       num_async_histogram_fetches_in_progress_(0),
       profiler_metrics_provider_(nullptr),
 #if defined(ENABLE_PLUGINS)
       plugin_metrics_provider_(nullptr),
 #endif
 #if defined(OS_WIN)
       google_update_metrics_provider_(nullptr),
 #endif
       drive_metrics_provider_(nullptr),
@@ skipping 460 matching lines @@
       break;
 
     default:
       NOTREACHED();
   }
 }
 
 void ChromeMetricsServiceClient::OnURLOpenedFromOmnibox(OmniboxLog* log) {
   metrics_service_->OnApplicationNotIdle();
 }