[WebSocket] Merge duplicated HTTP headers for devtools

Source/platform/network/WebSocketHandshakeResponse.cpp

Index: Source/platform/network/WebSocketHandshakeResponse.cpp
diff --git a/Source/platform/network/WebSocketHandshakeResponse.cpp b/Source/platform/network/WebSocketHandshakeResponse.cpp
index 0ad1670277e6de3a09c54a59aa20b617d15d0d89..3627cb39bc6b78514eb88299e93b6f781031921b 100644
--- a/Source/platform/network/WebSocketHandshakeResponse.cpp
+++ b/Source/platform/network/WebSocketHandshakeResponse.cpp
@@ -31,6 +31,7 @@
 #include "config.h"
 #include "platform/network/WebSocketHandshakeResponse.h"
 
+#include "platform/network/WebSocketHandshakeRequest.h"
 #include "wtf/Assertions.h"
 #include "wtf/text/AtomicString.h"
 
@@ -72,7 +73,7 @@ const HTTPHeaderMap& WebSocketHandshakeResponse::headerFields() const
 
 void WebSocketHandshakeResponse::addHeaderField(const AtomicString& name, const AtomicString& value)
 {
-    m_headerFields.add(name, value);
+    WebSocketHandshakeRequest::addAndMergeHeader(&m_headerFields, name, value);
 }
 
 void WebSocketHandshakeResponse::clearHeaderFields()