RemoteRealtimeMediaSourceProxy::whenReady should support more than on…

…e callback

https://bugs.webkit.org/show_bug.cgi?id=265236
rdar://118709394

Reviewed by Jean-Yves Avenard.

CoreAudioCaptureSource::whenReady can support being called more than once.
Given this and given the name (whenReady), we should also have RemoteRealtimeMediaSourceProxy::whenReady handle this.

* Source/WebKit/WebProcess/cocoa/RemoteRealtimeMediaSourceProxy.cpp:
(WebKit::RemoteRealtimeMediaSourceProxy::whenReady):

Canonical link: https://commits.webkit.org/271073@main

Source/WebKit/WebProcess/cocoa/RemoteRealtimeMediaSourceProxy.cpp

@@ -169,6 +169,13 @@ void RemoteRealtimeMediaSourceProxy::whenReady(CompletionHandler<void(WebCore::C
     if (m_isReady)
         return callback(WebCore::CaptureSourceError(m_failureReason));
 
+    if (m_callback) {
+        callback = [previousCallbacks = std::exchange(m_callback, { }), newCallback = WTFMove(callback)] (auto&& error) mutable {
+            previousCallbacks(WebCore::CaptureSourceError { error });
+            newCallback(WTFMove(error));
+        };
+    }
+
     m_callback = WTFMove(callback);
 }