Remove content dependencies from content settings providers.

chrome/browser/content_settings/host_content_settings_map.h

 // 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.
 
 // Maps hostnames to custom content settings.  Written on the UI thread and read
 // on any thread.  One instance per profile.
 
 #ifndef CHROME_BROWSER_CONTENT_SETTINGS_HOST_CONTENT_SETTINGS_MAP_H_
 #define CHROME_BROWSER_CONTENT_SETTINGS_HOST_CONTENT_SETTINGS_MAP_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
 #include "base/prefs/pref_change_registrar.h"
+#include "base/threading/non_thread_safe.h"
 #include "base/threading/platform_thread.h"
 #include "base/tuple.h"
 #include "chrome/browser/content_settings/content_settings_override_provider.h"
 #include "components/content_settings/core/browser/content_settings_observer.h"
 #include "components/content_settings/core/common/content_settings.h"
 #include "components/content_settings/core/common/content_settings_pattern.h"
 #include "components/content_settings/core/common/content_settings_types.h"
 
 class ExtensionService;
 class GURL;
@@ skipping 10 matching lines @@
 class ProviderInterface;
 class PrefProvider;
 }
 
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
 
 class HostContentSettingsMap
     : public content_settings::Observer,
+      public base::NonThreadSafe,

[blundell, 2014/09/23 07:27:00]

This is odd. base::NonThreadSafe directly above base::RefCountedThreadSafe?

[Bernhard Bauer, 2014/09/23 10:08:19]

:D

It's actually not that uncommon, it just looks a bit strange:
RefCountedThreadSafe doesn't mean that the object itself is thread-safe, just
that the refcounting is. There are classes that should only be used on a single
thread but have thread-safe refcounting to allow passing them to other threads.

In this case though, HostContentSettingsMap can be used on multiple threads,
it's just the setter methods that are UI-thread only. So NonThreadSafe would be
somewhat misleading.

[Jun Mukai, 2014/09/23 20:48:44]

Or simply add ThreadChecker as a field instead (as vabr suggested in .cc file).
Which is better?

       public base::RefCountedThreadSafe<HostContentSettingsMap> {
  public:
   enum ProviderType {
     // EXTENSION names is a layering violation when this class will move to
     // components.
     // TODO(mukai): find the solution.
     INTERNAL_EXTENSION_PROVIDER = 0,
     POLICY_PROVIDER,
     CUSTOM_EXTENSION_PROVIDER,
     OVERRIDE_PROVIDER,
@@ skipping 294 matching lines @@
   // time and by RegisterExtensionService, both of which should happen
   // before any other uses of it.
   ProviderMap content_settings_providers_;
 
   ObserverList<content_settings::Observer> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(HostContentSettingsMap);
 };
 
 #endif  // CHROME_BROWSER_CONTENT_SETTINGS_HOST_CONTENT_SETTINGS_MAP_H_