Load shelf preferences from ChromeLauncherController::AttachProfile.

chrome/browser/ui/ash/chrome_launcher_prefs.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/ash/chrome_launcher_prefs.h"
 
 #include <stddef.h>
 
 #include <set>
 
@@ skipping 96 matching lines @@
 }
 
 // Sets the preference value for the display with the given |display_id|.
 void SetPerDisplayPref(PrefService* prefs,
                        int64_t display_id,
                        const char* pref_key,
                        const std::string& value) {
   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;
   std::string key = base::Int64ToString(display_id);
   if (!shelf_prefs->GetDictionary(key, &pref_dictionary)) {
     pref_dictionary = new base::DictionaryValue();
     shelf_prefs->Set(key, pref_dictionary);

[James Cook, 2017/01/19 01:54:25]

Do we rely on this side-effect to create the new prefs dictionary for a new
display?

It looks like maybe if there's a pref with the same name on the primary display,
if you early-exit on GetPerDisplayPref then it might not create the new
dictionary.

[msw, 2017/01/19 02:19:15]

Hmm, good question... it would probably be more prudent to only bail if the
specific per-display preference is already set to the supplied value... I'll try
to work on this tonight or tomorrow, but I'll be on the road to Tahoe and
probably taking off a day or two.

   }
   pref_dictionary->SetStringWithoutPathExpansion(pref_key, value);
 }
 
 ShelfAlignment AlignmentFromPref(const std::string& value) {
   if (value == kShelfAlignmentLeft)
     return SHELF_ALIGNMENT_LEFT;
   else if (value == kShelfAlignmentRight)
     return SHELF_ALIGNMENT_RIGHT;
   // Default to bottom.
@@ skipping 605 matching lines @@
     pin_position = position_before.CreateAfter();
   else if (position_after.IsValid())
     pin_position = position_after.CreateBefore();
   else
     pin_position = syncer::StringOrdinal::CreateInitialOrdinal();
   app_service->SetPinPosition(app_launcher_id_str, pin_position);
 }
 
 }  // namespace launcher
 }  // namespace ash