[Clean up] Move VariationsHttpHeaderProvider into a subdirectory.

components/omnibox/BUILD.gn

 # Copyright 2014 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.
 
 static_library("omnibox") {
   sources = [
     "answers_cache.h",
     "answers_cache.cc",
     "autocomplete_input.cc",
     "autocomplete_input.h",
@@ skipping 27 matching lines @@
   public_deps = [
     "//components/metrics/proto",
   ]
   deps = [
     "//base",
     "//components/resources",
     "//components/search_engines",
     "//components/strings",
     "//components/url_fixer",
     "//components/variations",
+    "//components/variations/net:variations_http_provider",
     "//net",
     "//ui/base",
     "//url",
   ]
 }
 
 static_library("test_support") {
   sources = [
     "test_scheme_classifier.cc",
     "test_scheme_classifier.h",
@@ skipping 18 matching lines @@
     "omnibox_field_trial_unittest.cc",
   ]
 
   deps = [
     ":omnibox",
     ":test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }