Continuation of CL 5685007, rename the singleton accessor method in more files.

chrome/browser/chromeos/login/existing_user_controller.cc

Index: chrome/browser/chromeos/login/existing_user_controller.cc
diff --git a/chrome/browser/chromeos/login/existing_user_controller.cc b/chrome/browser/chromeos/login/existing_user_controller.cc
index 9718534e801e930ef988fbfb8f3d6144019b9299..2e43129b2fc741f2ef7379d1f6143d6aeb8beb0d 100644
--- a/chrome/browser/chromeos/login/existing_user_controller.cc
+++ b/chrome/browser/chromeos/login/existing_user_controller.cc
@@ -192,7 +192,7 @@ void ExistingUserController::Init() {
 
   EnableTooltipsIfNeeded(controllers_);
 
-  WmMessageListener::instance()->AddObserver(this);
+  WmMessageListener::GetInstance()->AddObserver(this);
 
   LoginUtils::Get()->PrewarmAuthentication();
   if (CrosLibrary::Get()->EnsureLoaded())
@@ -240,7 +240,7 @@ ExistingUserController::~ExistingUserController() {
   if (background_window_)
     background_window_->Close();
 
-  WmMessageListener::instance()->RemoveObserver(this);
+  WmMessageListener::GetInstance()->RemoveObserver(this);
 
   STLDeleteElements(&controllers_);
 }