ProtocolServer: Support request headers

You can now pass a dictionary of request headers when starting a new
download in ProtocolServer.

The HTTP and HTTPS protocol will include the headers in their requests.

Libraries/LibHTTP/HttpRequest.cpp

@@ -71,7 +71,14 @@ ByteBuffer HttpRequest::to_raw_request() const
     }
     builder.append(" HTTP/1.1\r\nHost: ");
     builder.append(m_url.host());
-    builder.append("\r\nConnection: close\r\n\r\n");
+    builder.append("\r\n");
+    for (auto& header : m_headers) {
+        builder.append(header.name);
+        builder.append(": ");
+        builder.append(header.value);
+        builder.append("\r\n");
+    }
+    builder.append("Connection: close\r\n\r\n");
     return builder.to_byte_buffer();
 }
 
@@ -181,4 +188,10 @@ Optional<HttpRequest> HttpRequest::from_raw_request(const ByteBuffer& raw_reques
     return request;
 }
 
+void HttpRequest::set_headers(const HashMap<String,String>& headers)
+{
+    for (auto& it : headers)
+        m_headers.append({ it.key, it.value });
+}
+
 }