Don't animate the default/background layer if there is no background.

chrome/browser/chromeos/login/base_login_display_host.cc

Index: chrome/browser/chromeos/login/base_login_display_host.cc
diff --git a/chrome/browser/chromeos/login/base_login_display_host.cc b/chrome/browser/chromeos/login/base_login_display_host.cc
index 9e44d640999582798342cdcdb0273b4fd98fb46f..c560d41acd38062ed9041e632d33b366c48db692 100644
--- a/chrome/browser/chromeos/login/base_login_display_host.cc
+++ b/chrome/browser/chromeos/login/base_login_display_host.cc
@@ -328,6 +328,14 @@ void BaseLoginDisplayHost::StartAnimation() {
       base::TimeDelta::FromMilliseconds(kLoginFadeoutTransitionDurationMs));
   layer->SetOpacity(0.0f);
 
+  if (ash::Shell::GetInstance()->GetContainer(
+          ash::internal::kShellWindowId_DesktopBackgroundContainer)->
+          children().empty()) {
+    // If there is no background window, don't perform any animation on the
+    // default and and background layer because there is nothing behind it.

[James Cook, 2012/01/13 01:06:51]

"and and" -> "and" (or maybe "or" :-)

[oshima, 2012/01/13 01:12:01]

oops, sorry. done.

+    return;
+  }
+
   // Background animation.
   if (kEnableBackgroundAnimation) {
     ui::Transform background_transform;