Split up ios/web:test_support.

ios/web/public/test/response_providers/error_page_response_provider.mm

-// 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/web/public/test/response_providers/error_page_response_provider.h"
-
-#include "base/logging.h"
-#import "ios/web/public/test/http_server.h"
-#include "net/http/http_status_code.h"
-
-// static
-GURL ErrorPageResponseProvider::GetDnsFailureUrl() {
-  return GURL("http://mock/bad");
-}
-
-// static
-GURL ErrorPageResponseProvider::GetRedirectToDnsFailureUrl() {
-  return web::test::HttpServer::MakeUrl("http://mock/redirect");
-}
-
-// Returns true for |RedirectToDnsFailureUrl|.
-bool ErrorPageResponseProvider::CanHandleRequest(const Request& request) {
-  return (HtmlResponseProvider::CanHandleRequest(request) ||
-          request.url ==
-              ErrorPageResponseProvider::GetRedirectToDnsFailureUrl());
-}
-
-void ErrorPageResponseProvider::GetResponseHeadersAndBody(
-    const Request& request,
-    scoped_refptr<net::HttpResponseHeaders>* headers,
-    std::string* response_body) {
-  if (HtmlResponseProvider::CanHandleRequest(request)) {
-    HtmlResponseProvider::GetResponseHeadersAndBody(request, headers,
-                                                    response_body);
-  } else if (request.url == GetRedirectToDnsFailureUrl()) {
-    *headers = web::ResponseProvider::GetRedirectResponseHeaders(
-        ErrorPageResponseProvider::GetDnsFailureUrl().spec(), net::HTTP_FOUND);
-  } else {
-    NOTREACHED();
-  }
-}