Refactor wait_util so it isn't coupled to EarlGrey.

ios/web/shell/test/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.
 
 import("//ios/build/config.gni")
 import("//ios/third_party/earl_grey/ios_eg_test.gni")
 
 ios_eg_test("ios_web_shell_test") {
   sources = [
     "context_menu_egtest.mm",
     "meta_tags_egtest.mm",
     "navigation_egtest.mm",
     "page_state_egtest.mm",
     "pdf_egtest.mm",
     "plugin_placeholder_egtest.mm",
     "redirect_egtest.mm",
   ]
 
   deps = [
     "//base",
     "//base/test:test_support",
+    "//ios/testing:ios_test_support",
     "//ios/testing/earl_grey:earl_grey_support",
     "//ios/web:earl_grey_test_support",
     "//ios/web:test_support",
     "//ios/web/shell",
     "//ios/web/shell/test:earl_grey_test_support",
     "//net:net",
     "//url:url",
 
     # All shared libraries must have the sanitizer deps to properly link in
     # asan mode (this target will be empty in other cases).
     "//build/config/sanitizers:deps",
   ]
 
   bundle_deps = [ ":bundle" ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
 
   assert_no_deps = ios_assert_no_deps
 }
 
 source_set("earl_grey_test_support") {
   testonly = true
 
   deps = [
     "//base",
     "//base/test:test_support",
+    "//ios/testing:ios_test_support",
     "//ios/testing/earl_grey:earl_grey_support",
     "//ios/third_party/earl_grey",
     "//ios/web",
     "//ios/web:earl_grey_test_support",
     "//ios/web:test_support",
     "//ios/web/shell",
     "//url",
   ]
 
   public_deps = [
@@ skipping 23 matching lines @@
   sources = [
     "http_server_files/basic_navigation_test.html",
     "http_server_files/tall_page.html",
     "http_server_files/testpage.pdf",
   ]
   outputs = [
     "{{bundle_resources_dir}}/{{source_root_relative_dir}}/" +
         "{{source_file_part}}",
   ]
 }