Merge 159996 - Fix bug with login-prompt-visible not being sent in some rare cases.

chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
===================================================================
--- chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc	(revision 160993)
+++ chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc	(working copy)
@@ -1009,6 +1009,7 @@
 
 void SigninScreenHandler::HandleAccountPickerReady(
     const base::ListValue* args) {
+  LOG(INFO) << "Login WebUI >> AccountPickerReady";
 
   PrefService* prefs = g_browser_process->local_state();
   if (prefs->GetBoolean(prefs::kFactoryResetRequested)) {
@@ -1139,8 +1140,14 @@
 }
 
 void SigninScreenHandler::HandleLoginVisible(const base::ListValue* args) {
-  LOG(INFO) << "Login WebUI >> LoginVisible, webui_visible_: "
-            << webui_visible_;
+  std::string source;
+  if (!args->GetString(0, &source)) {
+    NOTREACHED();
+    return;
+  }
+
+  LOG(INFO) << "Login WebUI >> LoginVisible, source: " << source
+            << ", webui_visible_: " << webui_visible_;
   if (!webui_visible_) {
     // There might be multiple messages from OOBE UI so send notifications after
     // the first one only.