Accessibility manager shouldn't try to access ash Shelf from login screen.

chrome/browser/chromeos/accessibility/accessibility_manager.cc

 // Copyright (c) 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/chromeos/accessibility/accessibility_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <utility>
 
@@ skipping 347 matching lines @@
     const PrefService::Preference* pref = ProfileHelper::GetSigninProfile()->
         GetPrefs()->FindPreference(pref_path_);
     if (!pref || !pref->IsUserControlled())
       return;
 
     // Copy the pref value from the signin screen.
     const base::Value* value_on_login = pref->GetValue();
     PrefService* user_prefs = current_profile->GetPrefs();
     user_prefs->Set(pref_path_, *value_on_login);
   }
+
+  // Update the panel height in the shelf layout manager when the profile
+  // changes, since the shelf layout manager doesn't exist in the login profile.
+  if (g_accessibility_manager)
+    g_accessibility_manager->UpdateChromeVoxPanelHeight();

[xiyuan, 2016/03/28 22:35:56]

Do this in AccessibilityManager::SetProfile so that we only do it once per
profile change?

[dmazzoni, 2016/03/29 20:43:22]

Done.

 }
 
 ///////////////////////////////////////////////////////////////////////////////
 //
 // AccessibilityManager
 
 // static
 void AccessibilityManager::Initialize() {
   CHECK(g_accessibility_manager == NULL);
   g_accessibility_manager = new AccessibilityManager();
@@ skipping 1041 matching lines @@
   ash::PlaySystemSoundAlways(SOUND_SPOKEN_FEEDBACK_DISABLED);
   // Clear the accessibility focus ring.
   AccessibilityFocusRingController::GetInstance()->SetFocusRing(
       std::vector<gfx::Rect>());
 }
 
 void AccessibilityManager::OnChromeVoxPanelClosing() {
   aura::Window* root_window = chromevox_panel_->GetRootWindow();
   chromevox_panel_widget_observer_.reset(nullptr);
   chromevox_panel_ = nullptr;
-  ash::Shelf::ForWindow(root_window)
-      ->shelf_layout_manager()
-      ->SetChromeVoxPanelHeight(0);
+
+  ash::Shelf* shelf = ash::Shelf::ForWindow(root_window);
+  if (!shelf)
+    return;
+
+  ash::ShelfLayoutManager* shelf_layout_manager = shelf->shelf_layout_manager();
+  if (shelf_layout_manager)
+    shelf_layout_manager->SetChromeVoxPanelHeight(0);
 }
 
 void AccessibilityManager::OnChromeVoxPanelDestroying() {
   chromevox_panel_widget_observer_.reset(nullptr);
   chromevox_panel_ = nullptr;
 }
 
+void AccessibilityManager::UpdateChromeVoxPanelHeight() {
+  if (chromevox_panel_)
+    chromevox_panel_->UpdatePanelHeight();
+}
+
 void AccessibilityManager::SetKeyboardListenerExtensionId(
     const std::string& id,
     content::BrowserContext* context) {
   keyboard_listener_extension_id_ = id;
 
   extensions::ExtensionRegistry* registry =
       extensions::ExtensionRegistry::Get(context);
   if (!extension_registry_observer_.IsObserving(registry) && !id.empty())
     extension_registry_observer_.Add(registry);
 }
 
 }  // namespace chromeos