Add a window property to associate RWHVA with its child AX tree ID

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index 1000c12f3f4f68d67ca1f1d5ad571e50f92963a4..4acaf33652024e6be8d54b40ed1aa0f9192ba674 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -63,6 +63,7 @@
 #include "services/ui/public/interfaces/window_manager_constants.mojom.h"
 #include "third_party/WebKit/public/platform/WebInputEvent.h"
 #include "third_party/WebKit/public/web/WebCompositionUnderline.h"
+#include "ui/accessibility/platform/aura_window_properties.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/client/cursor_client_observer.h"
@@ -1151,6 +1152,11 @@ RenderWidgetHostViewAura::AccessibilityGetNativeViewAccessible() {
   return NULL;
 }
 
+void RenderWidgetHostViewAura::SetMainFrameAXTreeID(
+    ui::AXTreeIDRegistry::AXTreeID id) {
+  window_->SetProperty(ui::kChildAXTreeID, id);
+}
+
 bool RenderWidgetHostViewAura::LockMouse() {
   return event_handler_->LockMouse();
 }