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

base/prefs/pref_service.cc

 // Copyright (c) 2012 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.
 
 #include "base/prefs/pref_service.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/default_pref_store.h"
 #include "base/prefs/pref_notifier_impl.h"
 #include "base/prefs/pref_registry.h"
 #include "base/prefs/pref_value_store.h"
 #include "base/stl_util.h"
 #include "base/string_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/value_conversions.h"
 #include "build/build_config.h"
 
-using content::BrowserContext;
-
 namespace {
 
 class ReadErrorHandler : public PersistentPrefStore::ReadErrorDelegate {
  public:
   ReadErrorHandler(base::Callback<void(PersistentPrefStore::PrefReadError)> cb)
       : callback_(cb) {}
 
   virtual void OnError(PersistentPrefStore::PrefReadError error) OVERRIDE {
     callback_.Run(error);
   }
@@ skipping 545 matching lines @@
       DCHECK(found_value->IsType(default_type));
       return found_value;
     } else {
       // Every registered preference has at least a default value.
       NOTREACHED() << "no valid value found for registered pref " << path;
     }
   }
 
   return NULL;
 }