Moves DCHECK so that it might actually hit

The way the DCHECKs are now we won't know if an associated interface
has been created. By moving the DCHECK earlier on we can know if that
is the cause.

BUG=626869
TEST=none
R=yzshen@chromium.org

Review-Url: https://codereview.chromium.org/2164133002
Cr-Commit-Position: refs/heads/master@{#406685}

services/ui/ws/window_tree.cc

@@ -1016,9 +1016,9 @@ void WindowTree::NewTopLevelWindow(
     uint32_t change_id,
     Id transport_window_id,
     mojo::Map<mojo::String, mojo::Array<uint8_t>> transport_properties) {
-  DCHECK(!waiting_for_top_level_window_info_);
   // TODO(sky): rather than DCHECK, have this kill connection.
   DCHECK(!window_manager_internal_);  // Not valid for the windowmanager.
+  DCHECK(!waiting_for_top_level_window_info_);
   const ClientWindowId client_window_id(transport_window_id);
   // TODO(sky): need a way for client to provide context to figure out display.
   Display* display = display_manager()->displays().empty()