cros: AutomationManagerAura::SendEvent crash fix

chrome/browser/ui/aura/accessibility/automation_manager_aura.cc

Index: chrome/browser/ui/aura/accessibility/automation_manager_aura.cc
diff --git a/chrome/browser/ui/aura/accessibility/automation_manager_aura.cc b/chrome/browser/ui/aura/accessibility/automation_manager_aura.cc
index a687ecb2fff448a30580103ede5ad53d071c17bb..7aa9d6feac5afb37700ff7634d315542f052f3d9 100644
--- a/chrome/browser/ui/aura/accessibility/automation_manager_aura.cc
+++ b/chrome/browser/ui/aura/accessibility/automation_manager_aura.cc
@@ -148,7 +148,8 @@ void AutomationManagerAura::SendEvent(BrowserContext* context,
   processing_events_ = true;
 
   ExtensionMsg_AccessibilityEventParams params;
-  if (!current_tree_serializer_->SerializeChanges(aura_obj, &params.update)) {
+  if (!current_tree_serializer_ ||

[dmazzoni, 2017/05/17 05:13:01]

Thanks for debugging! Looks like SendEvent was being
called before current_tree_serializer_ was first initialized.

Maybe move it up to the top, no log needed:

if (!current_tree_serializer_)
  return;

[Qiang(Joe) Xu, 2017/05/17 05:36:17]

Done.

+      !current_tree_serializer_->SerializeChanges(aura_obj, &params.update)) {
     LOG(ERROR) << "Unable to serialize one accessibility event.";
     return;
   }