Keep emtpy List/Dictionary pref value with non-empty default.

chrome/browser/ui/views/ash/launcher/chrome_launcher_delegate.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/views/ash/launcher/chrome_launcher_delegate.h"
 
 #include "ash/launcher/launcher_model.h"
 #include "ash/launcher/launcher_types.h"
 #include "ash/shell.h"
 #include "ash/wm/window_util.h"
@@ skipping 122 matching lines @@
   model_->RemoveObserver(this);
   for (IDToItemMap::iterator i = id_to_item_map_.begin();
        i != id_to_item_map_.end(); ++i) {
     model_->RemoveItemAt(model_->ItemIndexByID(i->first));
   }
   if (instance_ == this)
     instance_ = NULL;
 }
 
 void ChromeLauncherDelegate::Init() {
+  // TODO(xiyuan): Remove migration code and kUseDefaultPinnedApp after M20.
+  // Migration cases:
+  // - Users that unpin all apps:
+  //   - have default pinned apps
+  //   - kUseDefaultPinnedApps set to false
+  //   Migrate them by setting an empty list for kPinnedLauncherApps.
+  //
+  // - Users that have customized pinned apps:
+  //   - have non-default non-empty pinned apps list
+  //   - kUseDefaultPinnedApps set to false
+  //   Nothing needs to be done because customized pref overrides default.
+  //
+  // - Users that have default apps (i.e. new user or never pin/unpin):
+  //   - have default pinned apps
+  //   - kUseDefaultPinnedApps is still true
+  //   Nothing needs to be done because they should get the default.
+  if (profile_->GetPrefs()->FindPreference(
+          prefs::kPinnedLauncherApps)->IsDefaultValue() &&
+      !profile_->GetPrefs()->GetBoolean(prefs::kUseDefaultPinnedApps)) {
+    ListPrefUpdate updater(profile_->GetPrefs(), prefs::kPinnedLauncherApps);
+    updater.Get()->Clear();
+  }
+
   const base::ListValue* pinned_apps =
       profile_->GetPrefs()->GetList(prefs::kPinnedLauncherApps);
-
-  // Use default pinned apps only when current pinned apps list is empty and
-  // kUseDefaultPinnedApps is true.
-  // TODO(xiyuan): Remove this after http://crbug.com/122679 is resolved.
-  scoped_ptr<base::ListValue> default_pinned_apps;
-  if (pinned_apps->empty() &&
-      profile_->GetPrefs()->GetBoolean(prefs::kUseDefaultPinnedApps)) {
-    default_pinned_apps.reset(CreateDefaultPinnedAppsList());
-    pinned_apps = default_pinned_apps.get();
-  }
-
   for (size_t i = 0; i < pinned_apps->GetSize(); ++i) {
     DictionaryValue* app = NULL;
     if (pinned_apps->GetDictionary(i, &app)) {
       std::string app_id, type_string;
       if (app->GetString(kAppIDPath, &app_id) &&
           app->GetString(kAppTypePath, &type_string)) {
         AppType app_type;
         if (type_string == kAppTypeWindow)
           app_type = APP_TYPE_WINDOW;
         else if (type_string == kAppTypePanel)
@@ skipping 28 matching lines @@
 }
 
 // static
 void ChromeLauncherDelegate::RegisterUserPrefs(PrefService* user_prefs) {
   // TODO: If we want to support multiple profiles this will likely need to be
   // pushed to local state and we'll need to track profile per item.
   user_prefs->RegisterBooleanPref(prefs::kUseDefaultPinnedApps,
                                   true,
                                   PrefService::SYNCABLE_PREF);
   user_prefs->RegisterListPref(prefs::kPinnedLauncherApps,
+                               CreateDefaultPinnedAppsList(),
                                PrefService::SYNCABLE_PREF);
   user_prefs->RegisterStringPref(prefs::kShelfAutoHideBehavior,
                                  kShelfAutoHideBehaviorDefault,
                                  PrefService::SYNCABLE_PREF);
 }
 
 ash::LauncherID ChromeLauncherDelegate::CreateTabbedLauncherItem(
     LauncherUpdater* updater,
     IncognitoState is_incognito,
     ash::LauncherItemStatus status) {
@@ skipping 387 matching lines @@
   while (!pending_pinned_apps_.empty()) {
     const Item& item = pending_pinned_apps_.front();
 
     if (!app_icon_loader_->IsValidID(item.app_id))
       return;
 
     PinAppWithID(item.app_id, item.app_type);
     pending_pinned_apps_.pop();
   }
 }