[iOS Clean] Created OverlayService.

ios/clean/chrome/browser/ui/overlays/BUILD.gn

 # Copyright 2016 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.
 
-source_set("web_contents") {
+source_set("overlays") {
   sources = [
-    "web_contents_mediator.h",
-    "web_contents_mediator.mm",
-    "web_coordinator.h",
-    "web_coordinator.mm",
+    "overlay_coordinator.h",
+    "overlay_coordinator.mm",
+    "overlay_queue.h",
+    "overlay_queue.mm",
+    "overlay_scheduler.h",
+    "overlay_scheduler.mm",
   ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
 
   deps = [
-    ":web_contents_ui",
-    "//ios/chrome/browser",
+    "//base",
     "//ios/chrome/browser/web_state_list",
     "//ios/clean/chrome/browser/ui/commands",
-    "//ios/clean/chrome/browser/ui/context_menu",
     "//ios/shared/chrome/browser/ui/browser_list",
     "//ios/shared/chrome/browser/ui/commands",
     "//ios/shared/chrome/browser/ui/coordinators",
     "//ios/web",
-    "//ui/base",
-    "//url",
   ]
 }
 
-source_set("web_contents_ui") {
-  sources = [
-    "web_contents_consumer.h",
-    "web_contents_view_controller.h",
-    "web_contents_view_controller.mm",
-  ]
-
-  configs += [ "//build/config/compiler:enable_arc" ]
-}
-
 source_set("unit_tests") {
   testonly = true
   sources = [
-    "web_contents_mediator_unittest.mm",
+    "overlay_queue_unittest.mm",
   ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
 
   deps = [
-    ":web_contents",
-    ":web_contents_ui",
+    ":overlays",
     "//base",
     "//base/test:test_support",
     "//ios/chrome/browser/web_state_list",
     "//ios/chrome/browser/web_state_list:test_support",
     "//ios/chrome/test/base",
+    "//ios/clean/chrome/browser/ui/commands",
     "//ios/web/public/test/fakes",
     "//testing/gtest",
   ]
 }