Enable chrome.automation.getDesktop on all aura platforms.

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

Index: chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.cc
diff --git a/chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.cc b/chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.cc
index 366955d1a355431b1b4b6938a22822c83f22369b..4025d4edb85a475904683e213ef7c7e85d2760cf 100644
--- a/chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.cc
+++ b/chrome/browser/ui/ash/accessibility/ax_root_obj_wrapper.cc
@@ -8,12 +8,15 @@
 #include "base/strings/utf_string_conversions.h"
 #include "ui/accessibility/ax_node_data.h"
 #include "ui/accessibility/ax_view_state.h"
+#include "ui/aura/env.h"
 #include "ui/aura/window.h"
+#include "ui/aura/window_tree_host.h"
 #include "ui/views/accessibility/ax_aura_obj_cache.h"
 #include "ui/views/accessibility/ax_window_obj_wrapper.h"
 
 AXRootObjWrapper::AXRootObjWrapper(int32 id)
-    : id_(id), alert_window_(new aura::Window(NULL)) {
+    : id_(id), alert_window_(new aura::Window(NULL)), host_(NULL) {
+  aura::Env::GetInstance()->AddObserver(this);
 }
 
 AXRootObjWrapper::~AXRootObjWrapper() {
@@ -45,10 +48,14 @@ views::AXAuraObjWrapper* AXRootObjWrapper::GetParent() {
 
 void AXRootObjWrapper::GetChildren(
     std::vector<views::AXAuraObjWrapper*>* out_children) {
-  if (!ash::Shell::HasInstance())
+  if (!ash::Shell::HasInstance()) {
+    if (host_) {
+      out_children->push_back(
+          views::AXAuraObjCache::GetInstance()->GetOrCreate(host_->window()));
+    }
     return;

[sadrul, 2015/03/13 20:07:01]

This essentially means a WindowTreeHost was created before ash::Shell. Can you
clarify when that happens?

+oshima@ since I think it's a bug if this does in fact happen.

[oshima, 2015/03/13 20:40:03]

Yeah, this shouldn't happen (or you shouldn't try to access window before ash
shell is create, or after destroyed). Do you have a stack?

[David Tseng, 2015/03/13 21:33:53]

This code is meant to handle the linux/win case where USE_ASH is set but
shell::HasInstance() is false.

[oshima, 2015/03/13 21:58:47]

If that's the case, what you check screen type to tell if it's running on ash or
not.
(see gfx::Screen::GetScreenFor, and ScreenType in ui/gfx/screen_type_delegate.h)

[David Tseng, 2015/03/16 17:28:48]

To be clear, I need to know if shell exists in order to decide whether I can use
shell::GetAllRootWindows. So, I don't think checking screen type above achieves
this.

+  }
 
-  // Only on ash is there a notion of a root with children.
   aura::Window::Windows children =
       ash::Shell::GetInstance()->GetAllRootWindows();
   for (size_t i = 0; i < children.size(); ++i) {
@@ -70,3 +77,10 @@ void AXRootObjWrapper::Serialize(ui::AXNodeData* out_node_data) {
 int32 AXRootObjWrapper::GetID() {
   return id_;
 }
+
+void AXRootObjWrapper::OnWindowInitialized(aura::Window* window) {
+}
+
+void AXRootObjWrapper::OnHostActivated(aura::WindowTreeHost* host) {
+  host_ = host;

[dmazzoni, 2015/03/13 20:01:43]

Can't there be more than one WindowTreeHost, like if you have multiple monitors?

[oshima, 2015/03/13 20:40:03]

yes, that's correct.

[David Tseng, 2015/03/13 21:33:53]

EnvObserver is how I'm keeping track of things. I can't use shell since it
doesn't get instantiated on linux (and maybe win). What's the canonical  way to
do otherwise?

[oshima, 2015/03/13 21:58:47]

Can you explain how these wrapper objects are designed?

[David Tseng, 2015/03/16 17:00:52]

These wrappers adapt various objects in Aura for use in the ui/accessibility
module which provides serialization and semantics for accessibility of UI.

For the case of Ash + shell, the AXRootObjWrapper acts as the root of all
windows. Unfortunately, I haven't found a way to enumerate all windows on
non-shell platforms. On ash shell (Chrome OS), I use shell::GetAllRootWindows.

+}