[Blimp Engine] Adds a WindowTreeClient so that popup will have non-null paren…

blimp/engine/app/ui/BUILD.gn

Index: blimp/engine/app/ui/BUILD.gn
diff --git a/blimp/engine/app/ui/BUILD.gn b/blimp/engine/app/ui/BUILD.gn
deleted file mode 100644
index 444b910607b6bb820e69735a78c7faf15c49a411..0000000000000000000000000000000000000000
--- a/blimp/engine/app/ui/BUILD.gn
+++ /dev/null
@@ -1,29 +0,0 @@
-# Copyright 2015 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-import("//build/config/ui.gni")
-
-source_set("ui") {
-  sources = [
-    "blimp_layout_manager.cc",
-    "blimp_layout_manager.h",
-    "blimp_screen.cc",
-    "blimp_screen.h",
-    "blimp_window_tree_host.cc",
-    "blimp_window_tree_host.h",
-  ]
-
-  deps = [
-    "//blimp/common:blimp_common",
-    "//cc",
-    "//cc/surfaces",
-    "//ui/aura",
-    "//ui/compositor",
-    "//ui/events",
-    "//ui/gfx",
-    "//ui/platform_window",
-    "//ui/platform_window",
-    "//ui/platform_window/stub/",
-  ]
-}