Basic UkmService implementation

components/ukm/observers/history_delete_observer.h

+// 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_OBSERVERS_HISTORY_DELETE_OBSERVER_H_
+#define COMPONENTS_UKM_OBSERVERS_HISTORY_DELETE_OBSERVER_H_
+
+#include <set>
+
+#include "components/history/core/browser/history_service_observer.h"
+
+namespace ukm {
+
+// Observes multiple HistoryService objects for any events that delete history.
+// Handles cleanup and removing observers as objects are destroyed.
+class HistoryDeleteObserver : public history::HistoryServiceObserver {
+ public:
+  HistoryDeleteObserver();
+  ~HistoryDeleteObserver() override;
+
+  // Starts observing a service for history deletions.
+  void ObserveServiceForDeletions(history::HistoryService* history_service);
+
+  // history::HistoryServiceObserver
+  void OnURLsDeleted(history::HistoryService* history_service,
+                     bool all_history,
+                     bool expired,
+                     const history::URLRows& deleted_rows,
+                     const std::set<GURL>& favicon_urls) override;
+  void HistoryServiceBeingDeleted(
+      history::HistoryService* history_service) override;
+
+ protected:
+  virtual void OnHistoryDeleted() = 0;
+
+ private:
+  // Tracks observed history services, for cleanup.
+  std::set<history::HistoryService*> observed_history_services_;

[sdefresne, 2017/01/23 09:53:04]

I would recommend using ScopedObserver here. It already implements listening to
multiple object, and cleanup in its destructor (see base/scoped_observer.h).

  ScopedObserver<history::HistoryService, history::HistoryServiceObserver>
      scoped_observer_;

[Steven Holte, 2017/01/23 20:37:29]

Done, thanks for the tip.

+
+  DISALLOW_COPY_AND_ASSIGN(HistoryDeleteObserver);
+};
+
+}  // namespace ukm
+
+#endif  // COMPONENTS_UKM_OBSERVERS_HISTORY_DELETE_OBSERVER_H_