[websocket] Use HttpRequestHeaders, not string, to represent headers

net::WebSocketChannel and various related classes use std::string to
represent request headers. This CL changes them to HttpRequestHeaders.

Bug: 721400
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: Id730779b36f3a319a61b44516bd3e8389ebdfc23
Reviewed-on: https://chromium-review.googlesource.com/1065713
Reviewed-by: Kinuko Yasuda <[email protected]>
Reviewed-by: Adam Rice <[email protected]>
Commit-Queue: Yutaka Hirano <[email protected]>
Cr-Commit-Position: refs/heads/master@{#560888}
diff --git a/net/websockets/websocket_stream_create_test_base.h b/net/websockets/websocket_stream_create_test_base.h
index f0ac6fa..30a2f4ae 100644
--- a/net/websockets/websocket_stream_create_test_base.h
+++ b/net/websockets/websocket_stream_create_test_base.h
@@ -44,7 +44,7 @@
                               const std::vector<std::string>& sub_protocols,
                               const url::Origin& origin,
                               const GURL& site_for_cookies,
-                              const std::string& additional_headers,
+                              const HttpRequestHeaders& additional_headers,
                               std::unique_ptr<base::Timer> timer);
 
   static std::vector<HeaderKeyValuePair> RequestHeadersToVector(