[wpiutil] Add HttpWebSocketServerConnection (#2505)

This is a derived class of HttpServerConnection that implements the
WebSocket upgrade pieces.  This combination is pretty common so is
worth refactoring here.

wpiutil/src/test/native/cpp/HttpWebSocketServerConnectionTest.cpp

@@ -0,0 +1,28 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2020 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "wpi/HttpWebSocketServerConnection.h"  // NOLINT(build/include_order)
+
+#include <gtest/gtest.h>
+
+namespace wpi {
+
+class HttpWebSocketServerConnectionTest
+    : public HttpWebSocketServerConnection<HttpWebSocketServerConnectionTest> {
+ public:
+  HttpWebSocketServerConnectionTest(std::shared_ptr<uv::Stream> stream,
+                                    ArrayRef<StringRef> protocols)
+      : HttpWebSocketServerConnection{stream, protocols} {}
+
+  void ProcessRequest() override { ++gotRequest; }
+  void ProcessWsUpgrade() override { ++gotUpgrade; }
+
+  int gotRequest = 0;
+  int gotUpgrade = 0;
+};
+
+}  // namespace wpi