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..9d28f5202c736411a1a18950d7b83b6724a42a52 100644
--- a/chrome/browser/content_settings/host_content_settings_map.h
+++ b/chrome/browser/content_settings/host_content_settings_map.h
@@ -17,6 +17,7 @@
 #include "base/observer_list.h"
 #include "base/prefs/pref_change_registrar.h"
 #include "base/threading/platform_thread.h"
+#include "base/threading/thread_checker.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"
@@ -356,6 +357,8 @@ class HostContentSettingsMap
 
   ObserverList<content_settings::Observer> observers_;
 
+  base::ThreadChecker thread_checker_;
+
   DISALLOW_COPY_AND_ASSIGN(HostContentSettingsMap);
 };