Use StringPiece for CreateUploader/NetMetricsLogUploader params.

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 <set>
 #include <utility>
@@ skipping 495 matching lines @@
     // |FinishedReceivingProfilerData()| when the task completes.
     metrics::TrackingSynchronizer::FetchProfilerDataAsynchronously(
         weak_ptr_factory_.GetWeakPtr());
   } else {
     CollectFinalHistograms();
   }
 }
 
 std::unique_ptr<metrics::MetricsLogUploader>
 ChromeMetricsServiceClient::CreateUploader(
-    const std::string& server_url,
-    const std::string& mime_type,
+    base::StringPiece server_url,
+    base::StringPiece mime_type,
     metrics::MetricsLogUploader::MetricServiceType service_type,
     const base::Callback<void(int)>& on_upload_complete) {
   return std::unique_ptr<metrics::MetricsLogUploader>(
       new metrics::NetMetricsLogUploader(
           g_browser_process->system_request_context(), server_url, mime_type,
           service_type, on_upload_complete));
 }
 
 base::TimeDelta ChromeMetricsServiceClient::GetStandardUploadInterval() {
   return metrics::GetUploadInterval();
@@ skipping 432 matching lines @@
     ukm_service_->Purge();
     ukm_service_->ResetClientId();
   }
   // Signal service manager to enable/disable UKM based on new state.
   UpdateRunningServices();
 }
 
 bool ChromeMetricsServiceClient::IsHistorySyncEnabledOnAllProfiles() {
   return SyncDisableObserver::IsHistorySyncEnabledOnAllProfiles();
 }