[WIP] make GURL::path() return a StringPiece

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

 // Copyright 2015 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/file_based_response_provider_impl.h"
 
 #include "base/files/file_util.h"
 #include "ios/web/public/test/response_providers/response_provider.h"
 #include "url/gurl.h"
 
 namespace web {
 
 FileBasedResponseProviderImpl::FileBasedResponseProviderImpl(
     const base::FilePath& path)
     : path_(path) {}
 
 FileBasedResponseProviderImpl::~FileBasedResponseProviderImpl() {}
 
 bool FileBasedResponseProviderImpl::CanHandleRequest(
     const ResponseProvider::Request& request) {
   return base::PathExists(BuildTargetPath(request.url));
 }
 
 base::FilePath FileBasedResponseProviderImpl::BuildTargetPath(const GURL& url) {
   base::FilePath result = path_;
   const std::string kLocalhostHost = "localhost";
   if (url.host() != kLocalhostHost) {
     result = result.Append(url.host());
   }
-  std::string url_path = url.path();
+  std::string url_path = url.path().as_string();
   // Remove the leading slash in url path.
   if (url_path.length() > 0 && url_path[0] == '/') {
     url_path.erase(0, 1);
   }
   if (!url_path.empty())
     result = result.Append(url_path);
   return result;
 }
 
 }  // namespace web