[Extensions Toolbar] Make pref update non-destructive

chrome/browser/extensions/extension_toolbar_model.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/extensions/extension_toolbar_model.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/message_loop/message_loop.h"
@@ skipping 599 matching lines @@
   ExtensionIdList pref_positions = extension_prefs_->GetToolbarOrder();
   size_t pref_position_size = pref_positions.size();
   for (size_t i = 0; i < last_known_positions_.size(); ++i) {
     if (std::find(pref_positions.begin(), pref_positions.end(),
                   last_known_positions_[i]) == pref_positions.end()) {
       pref_positions.push_back(last_known_positions_[i]);
     }
   }
   last_known_positions_.swap(pref_positions);
 
-  // Clear out the old...
-  while (!toolbar_items_.empty()) {
-    scoped_refptr<const Extension> extension = toolbar_items_.back();
-    toolbar_items_.pop_back();
-    FOR_EACH_OBSERVER(Observer, observers_,
-                      OnToolbarExtensionRemoved(extension.get()));
-  }
-  DCHECK(toolbar_items_.empty());
-
-  // ...Add the new...
-  Populate(&last_known_positions_);
-
-  // ...And notify.
-  for (size_t i = 0; i < toolbar_items().size(); ++i) {
-    FOR_EACH_OBSERVER(Observer, observers_,
-                      OnToolbarExtensionAdded(toolbar_items()[i].get(), i));
+  int desired_index = 0;
+  // Loop over the updated list of last known positions, moving any extensions
+  // that are in the wrong place.
+  for (const std::string& id : last_known_positions_) {
+    int current_index = GetIndexForId(id);
+    if (current_index == -1)
+      continue;
+    if (current_index != desired_index) {
+      scoped_refptr<const Extension> extension = toolbar_items_[current_index];
+      toolbar_items_.erase(toolbar_items_.begin() + current_index);
+      toolbar_items_.insert(toolbar_items_.begin() + desired_index, extension);
+      // Notify the observers to keep them up-to-date.
+      FOR_EACH_OBSERVER(
+          Observer, observers_,
+          OnToolbarExtensionMoved(extension.get(), desired_index));
+    }
+    ++desired_index;
   }
 
   if (last_known_positions_.size() > pref_position_size) {
     // Need to update pref because we have extra icons. But can't call
     // UpdatePrefs() directly within observation closure.
     base::MessageLoop::current()->PostTask(
         FROM_HERE,
         base::Bind(&ExtensionToolbarModel::UpdatePrefs,
                    weak_ptr_factory_.GetWeakPtr()));
   }
@@ skipping 102 matching lines @@
     // Without the redesign, we only show extensions with browser actions.
     // Any extension without a browser action is an indication that we're
     // showing something new.
     if (!extension->manifest()->HasKey(manifest_keys::kBrowserAction))
       return true;
   }
   return false;
 }
 
 }  // namespace extensions