Use StringPiece for CreateUploader/NetMetricsLogUploader params.

ios/chrome/today_extension/today_metrics_logger.mm

 // 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.
 
 #import <UIKit/UIKit.h>
 
 #import "ios/chrome/today_extension/today_metrics_logger.h"
 
 #include "base/base64.h"
 #include "base/cpu.h"
@@ skipping 51 matching lines @@
   void SetMetricsClientId(const std::string& client_id) override;
   int32_t GetProduct() override;
   std::string GetApplicationLocale() override;
   bool GetBrand(std::string* brand_code) override;
   metrics::SystemProfileProto::Channel GetChannel() override;
   std::string GetVersionString() override;
   void InitializeSystemProfileMetrics(
       const base::Closure& done_callback) override;
   void CollectFinalMetricsForLog(const base::Closure& done_callback) override;
   std::unique_ptr<metrics::MetricsLogUploader> 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) override;
   base::TimeDelta GetStandardUploadInterval() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TodayMetricsServiceClient);
 };
 
 class TodayMetricsLog : public metrics::MetricsLog {
  public:
@@ skipping 59 matching lines @@
   NOTREACHED();
 }
 
 void TodayMetricsServiceClient::CollectFinalMetricsForLog(
     const base::Closure& done_callback) {
   NOTREACHED();
 }
 
 std::unique_ptr<metrics::MetricsLogUploader>
 TodayMetricsServiceClient::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) {
   NOTREACHED();
   return nullptr;
 }
 
 base::TimeDelta TodayMetricsServiceClient::GetStandardUploadInterval() {
   NOTREACHED();
   return base::TimeDelta::FromSeconds(0);
 }
@@ skipping 132 matching lines @@
 void TodayMetricsLogger::UniqueInconsistencyDetected(
     base::HistogramBase::Inconsistency problem) {
   UMA_HISTOGRAM_ENUMERATION("Histogram.InconsistenciesBrowserUnique", problem,
                             base::HistogramBase::NEVER_EXCEEDED_VALUE);
 }
 
 void TodayMetricsLogger::InconsistencyDetectedInLoggedCount(int amount) {
   UMA_HISTOGRAM_COUNTS("Histogram.InconsistentSnapshotBrowser",
                        std::abs(amount));
 }