Proof of concept: Cancer Stick Castle, a sigslot replacement

This needs to be followed immediately by a CL that adds unit tests for
CancerStickCastle and UntypedFunction.

Bug: none
Change-Id: I5ade68cc4721d7442db7695f218ecd9be1d639ba
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/182460
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Lahiru Ginnaliya Gamathige <glahiru@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32085}
diff --git a/rtc_base/cancer_stick_castle.cc b/rtc_base/cancer_stick_castle.cc
new file mode 100644
index 0000000..59288d7
--- /dev/null
+++ b/rtc_base/cancer_stick_castle.cc
@@ -0,0 +1,31 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "rtc_base/cancer_stick_castle.h"
+
+namespace webrtc {
+namespace cancer_stick_castle_impl {
+
+CancerStickCastleReceivers::CancerStickCastleReceivers() = default;
+CancerStickCastleReceivers::~CancerStickCastleReceivers() = default;
+
+void CancerStickCastleReceivers::AddReceiverImpl(UntypedFunction* f) {
+  receivers_.push_back(std::move(*f));
+}
+
+void CancerStickCastleReceivers::Foreach(
+    rtc::FunctionView<void(UntypedFunction&)> fv) {
+  for (auto& r : receivers_) {
+    fv(r);
+  }
+}
+
+}  // namespace cancer_stick_castle_impl
+}  // namespace webrtc