Make MetricsService upload logs through an interface.

components/metrics/metrics_log_uploader.h

Index: components/metrics/metrics_log_uploader.h
===================================================================
--- components/metrics/metrics_log_uploader.h	(revision 0)
+++ components/metrics/metrics_log_uploader.h	(working copy)
@@ -0,0 +1,26 @@
+// 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.
+
+#ifndef COMPONENTS_METRICS_METRICS_LOG_UPLOADER_H_
+#define COMPONENTS_METRICS_METRICS_LOG_UPLOADER_H_
+
+#include <string>
+
+#include "base/basictypes.h"
+
+namespace metrics {
+
+// Interface used by MetricsService to upload UMA logs.
+class MetricsLogUploader {
+ public:
+  virtual ~MetricsLogUploader() {}
+
+  // Uploads a log with the specified |log_data| and |log_hash|.
+  virtual bool UploadLog(const std::string& log_data,
+                         const std::string& log_hash) = 0;
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_METRICS_LOG_UPLOADER_H_