Basic UkmService implementation

components/ukm/ukm_pref_names.h

Index: components/ukm/ukm_pref_names.h
diff --git a/components/ukm/ukm_pref_names.h b/components/ukm/ukm_pref_names.h
new file mode 100644
index 0000000000000000000000000000000000000000..5d16f8da4d71e609d40e67b86649f866edd3f45c
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+++ b/components/ukm/ukm_pref_names.h
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+// 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_UKM_UKM_PREF_NAMES_H_
+#define COMPONENTS_UKM_UKM_PREF_NAMES_H_
+
+namespace ukm {
+namespace prefs {
+
+// Alphabetical list of preference names specific to the UKM
+// component. Keep alphabetized, and document each in the .cc file.
+extern const char kUkmClientId[];
+extern const char kUkmPersistedLogs[];
+
+}  // namespace prefs
+}  // namespace ukm
+
+#endif  // COMPONENTS_UKM_UKM_PREF_NAMES_H_