Improve existing lock transition - remove black splash.

ash/wm/power_button_controller.h

Index: ash/wm/power_button_controller.h
diff --git a/ash/wm/power_button_controller.h b/ash/wm/power_button_controller.h
index eee5f1cd9ee832ca9cd4509402e9f008eeddec70..9150d41d3cd8835117148e6d205ac0d3ab569700 100644
--- a/ash/wm/power_button_controller.h
+++ b/ash/wm/power_button_controller.h
@@ -57,7 +57,7 @@ class ASH_EXPORT PowerButtonController : public aura::RootWindowObserver,
   // Exposed here for TestApi::ContainerGroupIsAnimated().
   enum ContainerGroup {
     ALL_CONTAINERS = 0,
-    SCREEN_LOCKER_CONTAINERS,
+    SCREEN_LOCKER_CONTAINERS_EXCEPT_WALLPAPER,

[Daniel Erat, 2012/08/30 16:04:53]

I find this confusing.  The containers that each enum referred to was formerly
obvious:

ALL_CONTAINERS:
  kShellWindowId_NonLockScreenContainersContainer
  kShellWindowId_LockScreenContainersContainer
  kShellWindowId_LockScreenRelatedContainersContainer
SCREEN_LOCKER_CONTAINERS:
  kShellWindowId_LockScreenContainersContainer
SCREEN_LOCKER_AND_RELATED_CONTAINERS:
  kShellWindowId_LockScreenContainersContainer
  kShellWindowId_LockScreenRelatedContainersContainer
ALL_BUT_SCREEN_LOCKER_AND_RELATED_CONTAINERS:
  kShellWindowId_NonLockScreenContainersContainer

Just from looking at the enum names now, though, I have no idea which containers
are included in each.

Maybe it'd be better to make a bitmap instead so it's clear from the code which
containers are being affected (we'll end up with very long enum names,
otherwise):

  const int kNonLockScreenContainersMask = 1 << 0;
  const int kLockScreenContainersMask    = 1 << 1;
  // etc.

  StartAnimation(
      kLockScreenWallpaperMask |
      kLockScreenContainersMask |
      kLockScreenRelatedContainersMask,
      ANIMATION_HIDE);

[Nikita (slow), 2012/08/30 17:04:51]

Are you proposing to abandon those predefined groups completely?

[Daniel Erat, 2012/08/30 17:08:43]

Yes, if the concepts of which containers each group contains become so
complicated that they can't be described in fewer than 80 characters.

[Denis Kuznetsov (DE-MUC), 2012/08/30 17:15:04]

I think exclusion-based name like "non-something" or "all but something" are a
bit confusing - we just need some good term for containers with "user" windows -
ones we are hiding when locking screen. 

As for bitmaps, I find them confusing. With group constants, we have have just 4
possible outcomes, with bitmaps there would be at least 2^3 ("session" group,
"locked" group, "background") combinations -- harder to manage and test.

I think it's better to keep with enum, but rename constants to make them
clearer.

[Nikita (slow), 2012/09/03 14:50:59]

Done.

     SCREEN_LOCKER_AND_RELATED_CONTAINERS,
     ALL_BUT_SCREEN_LOCKER_AND_RELATED_CONTAINERS,
   };