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 "base/supports_user_data.h"
+#include "components/user_prefs/user_prefs_export.h"
+
+class PrefService;
+
+namespace content {
+class BrowserContext;
+}
+
+namespace components {
+
+// Components may use preferences associated with a given user. These
+// hang off of content::BrowserContext and can be retrieved using
+// UserPrefs::Get().
+//
+// It is up to the embedder tof create and own the PrefService and
+// attach it to BrowserContext using the UserPrefs::Set() function.
+class USER_PREFS_EXPORT UserPrefs : public base::SupportsUserData::Data {
+ public:
+  // Retrieves the PrefService for a given BrowserContext, or NULL if
+  // none is attached.
+  static PrefService* Get(content::BrowserContext* context);
+
+  // Hangs the specified |prefs| off of |context|. Should be called
+  // only once per BrowserContext.
+  static void Set(content::BrowserContext* context, PrefService* prefs);
+
+ private:
+  UserPrefs(PrefService* prefs);
+  virtual ~UserPrefs();
+
+  // Non-owning; owned by embedder.
+  PrefService* prefs_;
+
+  DISALLOW_COPY_AND_ASSIGN(UserPrefs);
+};
+
+}  // namespace components
+
+#endif  // COMPONENTS_USER_PREFS_USER_PREFS_H_