Watch the preferences for changes per profile instead of per tab.

chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc

Index: chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc
diff --git a/chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc b/chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc
index f894cc79b5edddc6a2d82b66512a00afed99a663..7e29f2bc06a7d2359cbb1d39e62a0155e86b6114 100644
--- a/chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc
+++ b/chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc
@@ -48,6 +48,7 @@
 #include "chrome/browser/ui/app_list/app_list_syncable_service_factory.h"
 #include "chrome/browser/ui/find_bar/find_bar_state_factory.h"
 #include "chrome/browser/ui/global_error/global_error_service_factory.h"
+#include "chrome/browser/ui/prefs/prefs_tab_helper.h"
 #include "chrome/browser/ui/tabs/pinned_tab_service_factory.h"
 #include "chrome/browser/ui/webui/ntp/ntp_resource_cache_factory.h"
 #include "chrome/browser/undo/bookmark_undo_service_factory.h"
@@ -233,6 +234,7 @@ EnsureBrowserContextKeyedServiceFactoriesBuilt() {
 #if defined(ENABLE_PLUGINS)
   PluginPrefsFactory::GetInstance();
 #endif
+  PrefsTabHelper::GetServiceInstance();

[Bernhard Bauer, 2015/01/28 23:35:52]

This isn't quite idiomatic; usually we expose the factory and call GetInstance()
directly. I'm personally not opposed to not exposing the factory, but seeing
this as it is right now still makes me do a double-take. Could we name the
method something like EnsureKeyedServiceInstanceCreated()? That way we
explicitly mention a KeyedService (as opposed to a generic "service", which
could be a lot of things), and if this method doesn't actually return anything,
naming it Get... is a bit weird.

   policy::ProfilePolicyConnectorFactory::GetInstance();
 #if defined(ENABLE_CONFIGURATION_POLICY)
 #if defined(OS_CHROMEOS)