Upstream ErrorPageResponseProvider to be used in integration tests.

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.
+
+#include "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();
+  }
+}