Test for task in front must include stack in front.

The CL that ensured that a dying task must be in front of the user
(ag/374996) only checked that the task was at the top of /a/ stack,
not on top of the frontmost stack. This checks the stack for being
frontmost before switching to home.

Fixes bug 11208762.

Change-Id: I43f6d380e7a880ec19db03711ada6c7437e15f73

services/java/com/android/server/am/ActivityStack.java

@@ -2628,7 +2628,7 @@ final class ActivityStack {
         if (task != null && task.removeActivity(r)) {
             if (DEBUG_STACK) Slog.i(TAG,
                     "removeActivityFromHistoryLocked: last activity removed from " + this);
-            if (task == topTask() && task.mOnTopOfHome) {
+            if (mStackSupervisor.isFrontStack(this) && task == topTask() && task.mOnTopOfHome) {
                 mStackSupervisor.moveHomeToTop();
             }
             mStackSupervisor.removeTask(task);