Move AccessibilityDelegate ownership to ash::WmShell

ash/common/wm_shell.cc

Index: ash/common/wm_shell.cc
diff --git a/ash/common/wm_shell.cc b/ash/common/wm_shell.cc
index bb012d7abb237310a4c141fbfe0bbdaf163b45e2..0bb9851c42ebbe41d4c0ed4e7cb60e16afa41a02 100644
--- a/ash/common/wm_shell.cc
+++ b/ash/common/wm_shell.cc
@@ -6,6 +6,7 @@
 
 #include <utility>
 
+#include "ash/common/accessibility_delegate.h"
 #include "ash/common/focus_cycler.h"
 #include "ash/common/keyboard/keyboard_ui.h"
 #include "ash/common/shell_delegate.h"
@@ -45,9 +46,15 @@ WmShell* WmShell::Get() {
 void WmShell::Initialize() {
   // Some delegates access WmShell during their construction. Create them here
   // instead of the WmShell constructor.
+  accessibility_delegate_.reset(delegate_->CreateAccessibilityDelegate());
   media_delegate_.reset(delegate_->CreateMediaDelegate());
 }
 
+void WmShell::Shutdown() {
+  // Accesses WmShell in its destructor.
+  accessibility_delegate_.reset();
+}
+
 void WmShell::OnMaximizeModeStarted() {
   FOR_EACH_OBSERVER(ShellObserver, shell_observers_, OnMaximizeModeStarted());
 }