Converts mash to use Shell

ash/display/window_tree_host_manager.cc

Index: ash/display/window_tree_host_manager.cc
diff --git a/ash/display/window_tree_host_manager.cc b/ash/display/window_tree_host_manager.cc
index f051cacaf7fe12a5d2819a8fc5954c5e646789a2..ec5943a8391666d1afac23c51236e1c8f045c200 100644
--- a/ash/display/window_tree_host_manager.cc
+++ b/ash/display/window_tree_host_manager.cc
@@ -356,22 +356,6 @@ AshWindowTreeHost* WindowTreeHostManager::GetAshWindowTreeHostForDisplayId(
   return host == window_tree_hosts_.end() ? nullptr : host->second;
 }
 
-void WindowTreeHostManager::CloseChildWindows() {
-  for (WindowTreeHostMap::const_iterator it = window_tree_hosts_.begin();
-       it != window_tree_hosts_.end(); ++it) {
-    aura::Window* root_window = GetWindow(it->second);
-    RootWindowController* controller = GetRootWindowController(root_window);
-    if (controller) {
-      controller->CloseChildWindows();
-    } else {
-      while (!root_window->children().empty()) {
-        aura::Window* child = root_window->children()[0];
-        delete child;
-      }
-    }
-  }
-}
-
 aura::Window::Windows WindowTreeHostManager::GetAllRootWindows() {
   aura::Window::Windows windows;
   for (WindowTreeHostMap::const_iterator it = window_tree_hosts_.begin();