Use StringPiece for CreateUploader/NetMetricsLogUploader params.

chrome/browser/metrics/chrome_metrics_service_client.cc

Index: chrome/browser/metrics/chrome_metrics_service_client.cc
diff --git a/chrome/browser/metrics/chrome_metrics_service_client.cc b/chrome/browser/metrics/chrome_metrics_service_client.cc
index 965168fed133c7d0f932b5d4c13b531fff0557b0..1897ae867e30bd82f3eb1fd73762bc429fc732b1 100644
--- a/chrome/browser/metrics/chrome_metrics_service_client.cc
+++ b/chrome/browser/metrics/chrome_metrics_service_client.cc
@@ -514,8 +514,8 @@ void ChromeMetricsServiceClient::CollectFinalMetricsForLog(
 
 std::unique_ptr<metrics::MetricsLogUploader>
 ChromeMetricsServiceClient::CreateUploader(
-    const std::string& server_url,
-    const std::string& mime_type,
+    const base::StringPiece& server_url,
+    const base::StringPiece& mime_type,
     metrics::MetricsLogUploader::MetricServiceType service_type,
     const base::Callback<void(int)>& on_upload_complete) {
   return std::unique_ptr<metrics::MetricsLogUploader>(