Refactor wait_util so it isn't coupled to EarlGrey.

ios/testing/earl_grey/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.
 
 config("earl_grey_support_config") {
   include_dirs = [ "." ]
   visibility = [ ":earl_grey_support" ]
 }
 
 source_set("earl_grey_support") {
   testonly = true
 
   deps = [
     "//base/test:test_support",
+    "//ios/testing:ios_test_support",
     "//ios/third_party/earl_grey",
   ]
 
   sources = [
     "disabled_test_macros.h",
     "matchers.h",
     "matchers.mm",
     "wait_util.h",
     "wait_util.mm",
   ]
 
   public_configs = [ ":earl_grey_support_config" ]
   configs += [ ":earl_grey_support_config" ]
 }