[ios] Use web_state_list in web_contents_mediator.

ios/clean/chrome/browser/ui/web_contents/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") {
   sources = [
     "web_contents_mediator.h",
     "web_contents_mediator.mm",
     "web_coordinator.h",
     "web_coordinator.mm",
   ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
 
   deps = [
     ":web_contents_ui",
     "//ios/shared/chrome/browser/coordinator_context",
+    "//ios/shared/chrome/browser/tabs",
+    "//ios/shared/chrome/browser/ui/browser_list",
     "//ios/shared/chrome/browser/ui/coordinators",
     "//ios/web",
     "//ui/base",
     "//url",
   ]
 }
 
 source_set("web_contents_ui") {
   sources = [
     "web_contents_consumer.h",
@@ skipping 11 matching lines @@
   ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
 
   deps = [
     ":web_contents",
     ":web_contents_ui",
     "//base",
     "//base/test:test_support",
     "//ios/chrome/test/base",
+    "//ios/shared/chrome/browser/tabs",
+    "//ios/shared/chrome/browser/tabs:test_support",
     "//ios/web:test_support",
     "//testing/gtest",
   ]
 }