Load shelf preferences from ChromeLauncherController::AttachProfile.

chrome/browser/ui/ash/chrome_launcher_prefs.cc

Index: chrome/browser/ui/ash/chrome_launcher_prefs.cc
diff --git a/chrome/browser/ui/ash/chrome_launcher_prefs.cc b/chrome/browser/ui/ash/chrome_launcher_prefs.cc
index 440f652a259c20d0f7200b68f58d2dd081fdc082..23ccb8e736b39bf36926f6934e356f10964016e5 100644
--- a/chrome/browser/ui/ash/chrome_launcher_prefs.cc
+++ b/chrome/browser/ui/ash/chrome_launcher_prefs.cc
@@ -114,6 +114,10 @@ void SetPerDisplayPref(PrefService* prefs,
   if (display_id < 0)
     return;
 
+  // Avoid DictionaryPrefUpdate's notifications for unchanged prefs.
+  if (GetPerDisplayPref(prefs, display_id, pref_key, pref_key) == value)
+    return;
+
   DictionaryPrefUpdate update(prefs, prefs::kShelfPreferences);
   base::DictionaryValue* shelf_prefs = update.Get();
   base::DictionaryValue* pref_dictionary = nullptr;