Fix Chrome OS virtual keyboard accessibility

ui/views/accessibility/ax_aura_obj_cache.cc

Index: ui/views/accessibility/ax_aura_obj_cache.cc
diff --git a/ui/views/accessibility/ax_aura_obj_cache.cc b/ui/views/accessibility/ax_aura_obj_cache.cc
index ad9df5c9fdd4d75a1b1e802c85352dd1de7f41f0..1f26711cd5890b33e04ccef088e497d5e5eda180 100644
--- a/ui/views/accessibility/ax_aura_obj_cache.cc
+++ b/ui/views/accessibility/ax_aura_obj_cache.cc
@@ -124,6 +124,12 @@ void AXAuraObjCache::OnFocusedViewChanged() {
     view->NotifyAccessibilityEvent(ui::AX_EVENT_FOCUS, true);
 }
 
+void AXAuraObjCache::FireEvent(AXAuraObjWrapper* aura_obj,
+                               ui::AXEvent event_type) {
+  if (delegate_)
+    delegate_->OnEvent(aura_obj, event_type);
+}
+
 AXAuraObjCache::AXAuraObjCache()
     : current_id_(1),
       focus_client_(nullptr),
@@ -181,6 +187,15 @@ void AXAuraObjCache::OnWindowDestroying(aura::Window* window) {
   focus_client_ = nullptr;
 }
 
+void AXAuraObjCache::OnWindowHierarchyChanged(

[David Tseng, 2017/04/17 15:39:54]

I don't know if this is what you really want. This |WindowObserver| gets added
on the focused root window. It's not added for all root windows. For that, you
would need the  activation client belonging to ash shell.

The focus client gets requested each time we use GetOrCreate. I'm really not
sure that's correct either since it depends on the next call to GetOrCreate
which might not happen if there were no events within the subtree for the
window.

I think what we need is for AutomationManagerAura to observe both focus client
and activation client from ash shell similar to compoents/exo/wm_helper_ ash.cc.
Doing it here would not be an option due to DEPS.

[dmazzoni, 2017/04/19 18:07:34]

So on Chrome OS, there's only one root window for each screen. We add an
observer for each root window as soon as we encounter it, and never remove
any observers for them, so I think it's reasonable to make use of
OnWindowHierarchyChanged here.

I filed http://crbug.com/713278 to track that.

Let me know if there's anything else I could make more clear in this change.

[David Tseng, 2017/04/19 19:21:31]

Please add a comment when we call root_window->AddObserver(this)

stating that |root_window| is the root of all Aura windows on a single screen.
It is equivalent to ash shell's primary root window when there is only one
screen.

That is not obvious to me, but that was my understanding from what you said
offline. Thanks.

[dmazzoni, 2017/04/19 21:37:02]

Done.

+    const HierarchyChangeParams& params) {
+  aura::Window* window = params.target;
+  if (window->parent()) {
+    delegate_->OnEvent(GetOrCreate(window->parent()),
+                       ui::AX_EVENT_CHILDREN_CHANGED);
+  }
+}
+
 template <typename AuraViewWrapper, typename AuraView>
 AXAuraObjWrapper* AXAuraObjCache::CreateInternal(
     AuraView* aura_view,