Remove the last usages of PrefObserver outside of Prefs.

chrome/browser/renderer_host/plugin_info_message_filter.cc

Index: chrome/browser/renderer_host/plugin_info_message_filter.cc
diff --git a/chrome/browser/renderer_host/plugin_info_message_filter.cc b/chrome/browser/renderer_host/plugin_info_message_filter.cc
index 6d5692325adc651e78f1dd17494b5449ee92da05..911e4cdc5a26997b40ea0f99b2ce644a3534f1b2 100644
--- a/chrome/browser/renderer_host/plugin_info_message_filter.cc
+++ b/chrome/browser/renderer_host/plugin_info_message_filter.cc
@@ -37,12 +37,12 @@ PluginInfoMessageFilter::Context::Context(int render_process_id,
       resource_context_(profile->GetResourceContext()),
       host_content_settings_map_(profile->GetHostContentSettingsMap()) {
   allow_outdated_plugins_.Init(prefs::kPluginsAllowOutdated,
-                               profile->GetPrefs(), NULL);
+                               profile->GetPrefs());
   allow_outdated_plugins_.MoveToThread(
       content::BrowserThread::GetMessageLoopProxyForThread(
           content::BrowserThread::IO));
   always_authorize_plugins_.Init(prefs::kPluginsAlwaysAuthorize,
-                                 profile->GetPrefs(), NULL);
+                                 profile->GetPrefs());
   always_authorize_plugins_.MoveToThread(
       content::BrowserThread::GetMessageLoopProxyForThread(
           content::BrowserThread::IO));