Remove content dependencies from content settings providers.

chrome/browser/content_settings/host_content_settings_map.h

Index: chrome/browser/content_settings/host_content_settings_map.h
diff --git a/chrome/browser/content_settings/host_content_settings_map.h b/chrome/browser/content_settings/host_content_settings_map.h
index dbe70c0d1338efa0a2685c37a16b9648c85e6696..665097691ee05a589b35999f2f1d8e9c4fc821e3 100644
--- a/chrome/browser/content_settings/host_content_settings_map.h
+++ b/chrome/browser/content_settings/host_content_settings_map.h
@@ -16,6 +16,7 @@
 #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"
@@ -46,6 +47,7 @@ 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 {