Introduce MetricsServiceClient and ChromeMetricsServiceClient.

components/metrics/metrics_service_client.h

Index: components/metrics/metrics_service_client.h
===================================================================
--- components/metrics/metrics_service_client.h	(revision 0)
+++ components/metrics/metrics_service_client.h	(working copy)
@@ -0,0 +1,35 @@
+// 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_SERVICE_CLIENT_H_
+#define COMPONENTS_METRICS_METRICS_SERVICE_CLIENT_H_
+
+#include <string>
+
+#include "base/basictypes.h"
+#include "components/metrics/proto/system_profile.pb.h"
+
+namespace metrics {
+
+// An abstraction of operations that depend on the embedder's (e.g. Chrome)
+// environment.
+class MetricsServiceClient {
+ public:
+  MetricsServiceClient();
+  virtual ~MetricsServiceClient();
+
+  virtual void SetClientID(const std::string& client_id) = 0;
+  virtual bool IsOffTheRecordSessionActive() = 0;

[Ilya Sherman, 2014/05/19 11:02:37]

nit: I think we prefer "Incognito" over "OffTheRecord" these days, to match the
feature name.

+  virtual std::string GetApplicationLocale() = 0;
+  virtual bool GetBrand(std::string* brand_code) = 0;
+  virtual SystemProfileProto::Channel GetChannel() = 0;
+  virtual std::string GetVersionString() = 0;

[Ilya Sherman, 2014/05/19 11:02:37]

Please document all of these methods.  Most will probably have trivial doc
strings, but some have less immediately obvious semantics and ordering
expectations, such as SetClientID().

[Alexei Svitkine (slow), 2014/05/19 11:43:25]

Done.

+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MetricsServiceClient);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_METRICS_SERVICE_CLIENT_H_