Pref service: expose all read-only PrefStores through Mojo

services/preferences/public/cpp/pref_store_adapter.h

Index: services/preferences/public/cpp/pref_store_adapter.h
diff --git a/services/preferences/public/cpp/pref_store_adapter.h b/services/preferences/public/cpp/pref_store_adapter.h
new file mode 100644
index 0000000000000000000000000000000000000000..c734606344e11151eda97c7c68b59e4978fde45a
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+++ b/services/preferences/public/cpp/pref_store_adapter.h
@@ -0,0 +1,44 @@
+// 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 SERVICES_PREFERENCES_PUBLIC_CPP_PREF_STORE_ADAPTER_H_
+#define SERVICES_PREFERENCES_PUBLIC_CPP_PREF_STORE_ADAPTER_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/values.h"
+#include "components/prefs/pref_store.h"
+#include "services/preferences/public/cpp/pref_store_impl.h"
+
+namespace prefs {
+
+// Ties the lifetime of a |PrefStoreImpl| to a |PrefStore|. Otherwise acts as a
+// |PrefStore|, forwarding all calls to the wrapped |PrefStore|.
+class PrefStoreAdapter : public PrefStore {
+ public:
+  PrefStoreAdapter(scoped_refptr<PrefStore> pref_store,
+                   std::unique_ptr<PrefStoreImpl> impl);
+
+  // PrefStore:
+  void AddObserver(PrefStore::Observer* observer) override;
+  void RemoveObserver(PrefStore::Observer* observer) override;
+  bool HasObservers() const override;
+  bool IsInitializationComplete() const override;
+  bool GetValue(const std::string& key,
+                const base::Value** result) const override;
+  std::unique_ptr<base::DictionaryValue> GetValues() const override;
+
+ private:
+  ~PrefStoreAdapter() override;
+
+  scoped_refptr<PrefStore> pref_store_;
+  std::unique_ptr<PrefStoreImpl> impl_;
+
+  DISALLOW_COPY_AND_ASSIGN(PrefStoreAdapter);
+};
+
+}  // namespace prefs
+
+#endif  // SERVICES_PREFERENCES_PUBLIC_CPP_PREF_STORE_ADAPTER_H_