Add skeletons for the factories to create the request coordinator and

components/offline_pages/background/offliner_factory.h

+// Copyright 2016 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_OFFLINE_PAGES_BACKGROUND_OFFLINER_FACTORY_H_
+#define COMPONENTS_OFFLINE_PAGES_BACKGROUND_OFFLINER_FACTORY_H_
+
+#include "base/macros.h"
+
+namespace offline_pages {
+
+class OfflinerPolicy;
+class Offliner;
+
+// An interface to a factory which can create a background offliner.
+// The returned factory is owned by the offliner, which is allowed to cache the

[Dmitry Titov, 2016/12/17 02:49:18]

This comment (and design of this factory) seems off. This is a factory that
creates offliners, not the other way around?

Also, if this factory returns a single cached offliner, then perhaps it is
possible to return naked pointer like here. If it ever can produce more then a
single cached instance of offliner, it has to return unique_ptr.

Given this design, it can only ever return a singleton cached pointer with
assumption that lifetime of consumer is guaranteed longer that this factory.
Since this factory is not a part of KeyedServices mechanism, there is no
explicit contract here for that lifetime assumption.

I think a better solution would be to either create an offliner directly and
pass it into RequestCoordinator (without having yet another factory that only
can produce a singleton), or go with the multiple offliners from the start and
return unique_ptr. Those offliners may share state or they may be independent,
separately.

+// factory and return it again later.
+class OfflinerFactory {
+ public:
+  OfflinerFactory() {}
+  virtual ~OfflinerFactory() {}
+
+  virtual Offliner* GetOffliner(const OfflinerPolicy* policy) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(OfflinerFactory);
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_BACKGROUND_OFFLINER_FACTORY_H_