Make MetricsService upload logs through an interface.

components/metrics/net/compression_utils.h

Index: components/metrics/net/compression_utils.h
===================================================================
--- components/metrics/net/compression_utils.h	(revision 0)
+++ components/metrics/net/compression_utils.h	(revision 0)
@@ -0,0 +1,17 @@
+// 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_NET_COMPRESSION_UTILS_H_
+#define COMPONENTS_METRICS_NET_COMPRESSION_UTILS_H_
+
+#include <string>
+
+namespace metrics {
+
+// Compresses the text in |input| using gzip, storing the result in |output|.
+bool GzipCompress(const std::string& input, std::string* output);
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_NET_COMPRESSION_UTILS_H_