cros: persistent window restores on active user session started

changes:
Using IsActiveUserSessionStarted instead of IsUserSessionBlocked as
IsUserSessionBlocked could contain not ACTIVE state during logging in,
which could cause BuildWindowList crash.

Bug: 805046
Test: tested on device
Change-Id: I13fac4df6a0dd7e531dc30fbc91d6dd80152ee30
Reviewed-on: https://chromium-review.googlesource.com/949666Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Qiang Xu <warx@google.com>
Cr-Commit-Position: refs/heads/master@{#540972}

ash/display/persistent_window_controller.cc

@@ -36,7 +36,7 @@ bool ShouldProcessWindowList() {
   }
 
   // Window cycle list exists in active user session only.
-  if (Shell::Get()->session_controller()->IsUserSessionBlocked())
+  if (!Shell::Get()->session_controller()->IsActiveUserSessionStarted())
     return false;
 
   if (GetDisplayManager()->IsInMirrorMode())