Improve existing lock transition - remove black splash.

ash/root_window_controller.cc

Index: ash/root_window_controller.cc
diff --git a/ash/root_window_controller.cc b/ash/root_window_controller.cc
index c6c047fa7dd6b2a2c5c5cc1af353e595ef320215..503bb419222282618ebc984f721cb4f23b7fd0f4 100644
--- a/ash/root_window_controller.cc
+++ b/ash/root_window_controller.cc
@@ -134,10 +134,26 @@ void CreateContainersInRootWindow(aura::RootWindow* root_window) {
   // of containers simultaneously without messing up the current transformations
   // on those containers.  These are direct children of the root window; all of
   // the other containers are their children.
+  // Desktop and lock screen background containers are not part of the
+  // lock animation so they are not included in those animate groups.
+
+  aura::Window* desktop_background_containers = CreateContainer(
+      internal::kShellWindowId_DesktopBackgroundContainer,
+      "DesktopBackgroundContainer",
+      root_window);
+  SetChildWindowVisibilityChangesAnimated(desktop_background_containers);
+
   aura::Window* non_lock_screen_containers = CreateContainer(
       internal::kShellWindowId_NonLockScreenContainersContainer,
       "NonLockScreenContainersContainer",
       root_window);
+
+  aura::Window* lock_background_containers = CreateContainer(

[Daniel Erat, 2012/09/04 16:58:59]

Nikita and I discussed this over IM.  I didn't think that this container is
necessary anymore; it seems like the wallpaper should just be able to always
stay in DesktopBackgroundContainer.  Apparently we want to move the wallpaper
here when the screen is locked to make sure that there's an opaque layer
occluding the non-lock-screen layers, though.  It'd be good to document this in
a comment somewhere.

[Nikita (slow), 2012/09/04 17:36:42]

Done.

+      internal::kShellWindowId_LockScreenBackgroundContainer,
+      "LockScreenBackgroundContainer",
+      root_window);
+  SetChildWindowVisibilityChangesAnimated(lock_background_containers);
+
   aura::Window* lock_screen_containers = CreateContainer(
       internal::kShellWindowId_LockScreenContainersContainer,
       "LockScreenContainersContainer",
@@ -154,12 +170,6 @@ void CreateContainersInRootWindow(aura::RootWindow* root_window) {
   CreateContainer(internal::kShellWindowId_SystemBackgroundContainer,
                   "SystemBackgroundContainer", non_lock_screen_containers);
 
-  aura::Window* desktop_background_containers = CreateContainer(
-      internal::kShellWindowId_DesktopBackgroundContainer,
-      "DesktopBackgroundContainer",
-      non_lock_screen_containers);
-  SetChildWindowVisibilityChangesAnimated(desktop_background_containers);
-
   aura::Window* default_container = CreateContainer(
       internal::kShellWindowId_DefaultContainer,
       "DefaultContainer",
@@ -211,13 +221,6 @@ void CreateContainersInRootWindow(aura::RootWindow* root_window) {
       non_lock_screen_containers);
   SetUsesScreenCoordinates(input_method_container);
 
-  aura::Window* lock_background_containers = CreateContainer(
-      internal::kShellWindowId_LockScreenBackgroundContainer,
-      "LockScreenBackgroundContainer",
-      lock_screen_containers);
-
-  SetChildWindowVisibilityChangesAnimated(lock_background_containers);
-
   // TODO(beng): Figure out if we can make this use
   // SystemModalContainerEventFilter instead of stops_event_propagation.
   aura::Window* lock_container = CreateContainer(