Basic UkmService implementation

components/ukm/BUILD.gn

Index: components/ukm/BUILD.gn
diff --git a/components/ukm/BUILD.gn b/components/ukm/BUILD.gn
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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.
+
+static_library("ukm") {
+  sources = [
+    "metrics_reporting_scheduler.cc",
+    "metrics_reporting_scheduler.h",
+    "persisted_logs_metrics_impl.cc",
+    "persisted_logs_metrics_impl.h",
+    "ukm_pref_names.cc",
+    "ukm_pref_names.h",
+    "ukm_service.cc",
+    "ukm_service.h",
+  ]
+
+  deps = [
+    "//base",
+    "//components/data_use_measurement/core",
+    "//components/metrics",
+    "//components/prefs",
+    "//components/variations",
+  ]
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "ukm_service_unittest.cc",
+  ]
+
+  deps = [
+    ":ukm",
+    "//base",
+    "//base/test:test_support",
+    "//components/metrics",
+    "//components/prefs:test_support",
+    "//net:test_support",
+    "//testing/gtest",
+    "//url",
+  ]
+}