Use StringPiece for CreateUploader/NetMetricsLogUploader params.

components/metrics/test_metrics_log_uploader.h

 // Copyright 2017 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 COMPONENTS_METRICS_TEST_METRICS_LOG_UPLOADER_H_
 #define COMPONENTS_METRICS_TEST_METRICS_LOG_UPLOADER_H_
 
 #include "components/metrics/metrics_log_uploader.h"
 
 namespace metrics {
 
 class TestMetricsLogUploader : public MetricsLogUploader {
  public:
-  TestMetricsLogUploader(const std::string& server_url,
-                         const std::string& mime_type,
-                         MetricsLogUploader::MetricServiceType service_type,
-                         const base::Callback<void(int)>& on_upload_complete);
+  explicit TestMetricsLogUploader(
+      const base::Callback<void(int)>& on_upload_complete);
   ~TestMetricsLogUploader() override;
 
   // Mark the current upload complete with the given response code.
   void CompleteUpload(int response_code);
 
   // Check if UploadLog has been called.
   bool is_uploading() const { return is_uploading_; }
 
  private:
   // MetricsLogUploader:
   void UploadLog(const std::string& compressed_log_data,
                  const std::string& log_hash) override;
 
+  const base::Callback<void(int)> on_upload_complete_;
   bool is_uploading_;
 
   DISALLOW_COPY_AND_ASSIGN(TestMetricsLogUploader);
 };
 
 }  // namespace metrics
 
 #endif  // COMPONENTS_METRICS_TEST_METRICS_LOG_UPLOADER_H_