Introduce //components/user_prefs, use to eliminate c/b/prefs dependency in Autofill.

components/user_prefs/user_prefs.h

+// Copyright 2013 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_USER_PREFS_USER_PREFS_H_
+#define COMPONENTS_USER_PREFS_USER_PREFS_H_
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "components/user_prefs/user_prefs_delegate.h"
+#include "components/user_prefs/user_prefs_export.h"
+
+template <typename T> struct DefaultSingletonTraits;
+class PrefService;
+
+namespace content {
+class BrowserContext;
+};
+
+namespace components {
+
+// Components may use preferences associated with a given user. These
+// are retrieved based on content::BrowserContext.
+//
+// This singleton is initialized by embedders, to provide other
+// components with a means of doing this lookup.
+class USER_PREFS_EXPORT UserPrefs {
+ public:
+  static UserPrefs* GetInstance();
+
+  ~UserPrefs() {}
+
+  // Must be called exactly once, before any other method calls on
+  // this object. This object takes ownership of the delegate.
+  void Initialize(scoped_ptr<UserPrefsDelegate> delegate);
+
+  // Retrieves the PrefService for the user preferences tied to the
+  // given BrowserContext. Returns NULL if there is no such
+  // PrefService, or if |Initialize| has not been called.
+  PrefService* Lookup(content::BrowserContext* context);

[Mattias Nissler (ping if slow), 2013/02/27 16:16:43]

I wonder whether you want to make a static helper for shortcutting this? Maybe:

components::UserPrefs::Get(context)

instead of:

components::UserPrefs::GetInstance()->Lookup(context)

I don't feel strong though. Your call.

+
+ private:
+  UserPrefs() {}
+  friend struct DefaultSingletonTraits<UserPrefs>;
+
+  scoped_ptr<UserPrefsDelegate> delegate_;
+
+  DISALLOW_COPY_AND_ASSIGN(UserPrefs);
+};
+
+}  // namespace components
+
+#endif  // COMPONENTS_USER_PREFS_USER_PREFS_H_