(Merge to M-51) Revise the shelf alignment locking mechanism.

chrome/browser/ui/ash/launcher/chrome_launcher_controller.cc

 // Copyright 2013 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/launcher/chrome_launcher_controller.h"
 
 #include <stddef.h>
 
 #include <vector>
 
@@ skipping 1146 matching lines @@
   switch (shelf->GetAlignment()) {
     case ash::SHELF_ALIGNMENT_BOTTOM:
       value = ash::kShelfAlignmentBottom;
       break;
     case ash::SHELF_ALIGNMENT_LEFT:
       value = ash::kShelfAlignmentLeft;
       break;
     case ash::SHELF_ALIGNMENT_RIGHT:
       value = ash::kShelfAlignmentRight;
       break;
+    case ash::SHELF_ALIGNMENT_BOTTOM_LOCKED:
+      // This should not be a valid preference option for now. We only want to
+      // lock the shelf during login or when adding a user.
+      return;
   }
 
   aura::Window* root_window =
       shelf->shelf_widget()->GetNativeWindow()->GetRootWindow();
 
   UpdatePerDisplayPref(profile_->GetPrefs(), root_window,
                        prefs::kShelfAlignment, value);
 
   if (root_window == ash::Shell::GetPrimaryRootWindow()) {
     // See comment in |kShelfAlignment| about why we have two prefs here.
@@ skipping 1051 matching lines @@
 
 AppIconLoader* ChromeLauncherController::GetAppIconLoaderForApp(
     const std::string& app_id) {
   for (const auto& app_icon_loader : app_icon_loaders_) {
     if (app_icon_loader->CanLoadImageForApp(app_id))
       return app_icon_loader.get();
   }
 
   return nullptr;
 }