Enable chrome.automation.getDesktop on all aura platforms.

chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.h

Index: chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.h
diff --git a/chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.h b/chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.h
index 017c0babb3d78e29d040614485aad3e5640c4749..1157ad066e914b7d2e2b5d571b4adef30ce8d933 100644
--- a/chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.h
+++ b/chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.h
@@ -8,13 +8,15 @@
 #include <string>
 
 #include "base/basictypes.h"
+#include "ui/aura/env_observer.h"
 #include "ui/views/accessibility/ax_aura_obj_wrapper.h"
 
 namespace aura {
 class Window;
 }  // namespace aura
 
-class AXRootObjWrapper : public views::AXAuraObjWrapper {
+class AXRootObjWrapper : public views::AXAuraObjWrapper,
+                         public aura::EnvObserver {
  public:
   explicit AXRootObjWrapper(int32 id);
   ~AXRootObjWrapper() override;
@@ -32,11 +34,17 @@ class AXRootObjWrapper : public views::AXAuraObjWrapper {
   void Serialize(ui::AXNodeData* out_node_data) override;
   int32 GetID() override;
 
+  // aura::EnvObserver overrides.
+  void OnWindowInitialized(aura::Window* window) override;
+  void OnHostActivated(aura::WindowTreeHost* host) override;
+
  private:
   int32 id_;
 
   aura::Window* alert_window_;
 
+  aura::WindowTreeHost* host_;
+
   DISALLOW_COPY_AND_ASSIGN(AXRootObjWrapper);
 };