[ macOS EWS ] media/video-remove-insert-repaints.html is a flaky crash

https://bugs.webkit.org/show_bug.cgi?id=260663
rdar://114387091

Reviewed by Jer Noble.

If VideoFullscreenManager::removeContext is called with a contextId that doesn't exist in
m_contextMap then a new model would be created with a null video element, leading to a crash when
attempting to remove the video element from m_videoElements. Addressed this by returning early in
VideoFullscreenManager::removeContext if no model/interface pair exists for the given contextId.
Assert that this does not occur to help us track down the underlying issue in Debug builds
(removeContext should not be called for a non-existent contextId).

* Source/WebKit/WebProcess/cocoa/PlaybackSessionManager.mm:
(WebKit::PlaybackSessionManager::removeContext):
* Source/WebKit/WebProcess/cocoa/VideoFullscreenManager.mm:
(WebKit::VideoFullscreenManager::removeContext):

Canonical link: https://commits.webkit.org/267257@main

Source/WebKit/WebProcess/cocoa/PlaybackSessionManager.mm

@@ -231,15 +231,23 @@
 
 void PlaybackSessionManager::removeContext(PlaybackSessionContextIdentifier contextId)
 {
-    auto& [model, interface] = ensureModelAndInterface(contextId);
+    auto [model, interface] = m_contextMap.get(contextId);
+    ASSERT(model);
+    ASSERT(interface);
+    if (!model || !interface)
+        return;
 
-    RefPtr<HTMLMediaElement> mediaElement = model->mediaElement();
-    model->setMediaElement(nullptr);
     model->removeClient(*interface);
     interface->invalidate();
-    if (mediaElement)
-        m_mediaElements.remove(*mediaElement);
     m_contextMap.remove(contextId);
+
+    RefPtr mediaElement = model->mediaElement();
+    ASSERT(mediaElement);
+    if (!mediaElement)
+        return;
+
+    model->setMediaElement(nullptr);
+    m_mediaElements.remove(*mediaElement);
 }
 
 void PlaybackSessionManager::addClientForContext(PlaybackSessionContextIdentifier contextId)

Source/WebKit/WebProcess/cocoa/VideoFullscreenManager.mm

@@ -206,16 +206,25 @@ static FloatRect inlineVideoFrame(HTMLVideoElement& element)
 
 void VideoFullscreenManager::removeContext(PlaybackSessionContextIdentifier contextId)
 {
-    auto [model, interface] = ensureModelAndInterface(contextId);
-
     m_playbackSessionManager->removeClientForContext(contextId);
 
-    RefPtr<HTMLVideoElement> videoElement = model->videoElement();
-    model->setVideoElement(nullptr);
+    auto [model, interface] = m_contextMap.get(contextId);
+    ASSERT(model);
+    ASSERT(interface);
+    if (!model || !interface)
+        return;
+
     model->removeClient(*interface);
     interface->invalidate();
-    m_videoElements.remove(*videoElement);
     m_contextMap.remove(contextId);
+
+    RefPtr videoElement = model->videoElement();
+    ASSERT(videoElement);
+    if (!videoElement)
+        return;
+
+    model->setVideoElement(nullptr);
+    m_videoElements.remove(*videoElement);
 }
 
 void VideoFullscreenManager::addClientForContext(PlaybackSessionContextIdentifier contextId)