Introduce window container to be used by lock screen app windows

ash/public/cpp/shell_window_ids.h

Index: ash/public/cpp/shell_window_ids.h
diff --git a/ash/public/cpp/shell_window_ids.h b/ash/public/cpp/shell_window_ids.h
index ab5a16840647c1a37abb98576acd4dedbbfc1aa4..972ebf0f9901844a4e6056708155e1d5d6bc6895 100644
--- a/ash/public/cpp/shell_window_ids.h
+++ b/ash/public/cpp/shell_window_ids.h
@@ -113,8 +113,20 @@ enum ShellWindowId {
   // The topmost container, used for power off animation.
   kShellWindowId_PowerButtonAnimationContainer,
 
+  // The containers for windows that handle lock tray actions (e.g. new note
+  // action). The action handler windows containers should be visible on lock
+  // screen, but only when an action is being handled. The container to which
+  // the action handler window should be added depends on the lock action state:
+  // * in active state, the window should be contained in
+  //   LockActionHandlerContainer, which is stacked over lock screen container.
+  // * in background state, the window should be container in
+  //   LockActinHandlerContainer_Background, which is stacked below lock screen
+  //   container.
+  kShellWindowId_LockActionHandlerContainer,
+  kShellWindowId_LockActionHandlerContainer_Background,
+
   kShellWindowId_Min = kShellWindowId_ScreenRotationContainer,
-  kShellWindowId_Max = kShellWindowId_PowerButtonAnimationContainer,
+  kShellWindowId_Max = kShellWindowId_LockActionHandlerContainer_Background,
 };
 
 // A list of all the above valid container IDs. Add any new ID to this list.
@@ -146,6 +158,8 @@ const int32_t kAllShellContainerIds[] = {
     kShellWindowId_PhantomWindow,
     kShellWindowId_MouseCursorContainer,
     kShellWindowId_PowerButtonAnimationContainer,
+    kShellWindowId_LockActionHandlerContainer,
+    kShellWindowId_LockActionHandlerContainer_Background,
 };
 
 // These are the list of container ids of containers which may contain windows