Safari crashes when remote video tiles are added or toggled

[justindarc]

Describe the bug
When in Safari, the browser tab will crash and reload the page when remote video tiles are added or toggled.

There are two different crash signatures for Safari that can be seen in the system logs:

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   com.apple.WebCore                 0x0000000102fab33c WebCore::MediaPlayerPrivateMediaStreamAVFObjC::sampleBufferUpdated(WebCore::MediaStreamTrackPrivate&, WebCore::MediaSample&) + 28
1   com.apple.WebCore                 0x000000010457036c WebCore::MediaStreamTrackPrivate::forEachObserver(WTF::Function<void (WebCore::MediaStreamTrackPrivate::Observer&)> const&) const + 652
2   com.apple.WebCore                 0x0000000104570b43 WebCore::MediaStreamTrackPrivate::videoSampleAvailable(WebCore::MediaSample&) + 259
3   com.apple.WebCore                 0x0000000104574d4c WebCore::RealtimeMediaSource::forEachObserver(WTF::Function<void (WebCore::RealtimeMediaSource::Observer&)> const&) const + 652
4   com.apple.WebCore                 0x0000000104575068 WebCore::RealtimeMediaSource::videoSampleAvailable(WebCore::MediaSample&) + 280
5   com.apple.WebCore                 0x000000010336a7a9 WTF::Detail::CallableWrapper<WebCore::RealtimeIncomingVideoSourceCocoa::OnFrame(webrtc::VideoFrame const&)::$_7, void>::call() + 265
6   com.apple.JavaScriptCore          0x00000004208f65f9 WTF::dispatchFunctionsFromMainThread() + 361
7   com.apple.Foundation              0x00007fff4e41b302 __NSThreadPerformPerform + 328
8   com.apple.CoreFoundation          0x00007fff4c13fde3 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
9   com.apple.CoreFoundation          0x00007fff4c13fd89 __CFRunLoopDoSource0 + 108
10  com.apple.CoreFoundation          0x00007fff4c12374b __CFRunLoopDoSources0 + 195
11  com.apple.CoreFoundation          0x00007fff4c122d15 __CFRunLoopRun + 1189
12  com.apple.CoreFoundation          0x00007fff4c12261e CFRunLoopRunSpecific + 455
13  com.apple.Foundation              0x00007fff4e38732f -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 280
14  com.apple.Foundation              0x00007fff4e387204 -[NSRunLoop(NSRunLoop) run] + 76
15  libxpc.dylib                      0x00007fff782b6077 _xpc_objc_main + 552
16  libxpc.dylib                      0x00007fff782b5b79 xpc_main + 433
17  com.apple.WebKit                  0x0000000101ea0e53 WebKit::XPCServiceMain(int, char const**) + 547
18  libdyld.dylib                     0x00007fff7807d3d5 start + 1

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   com.apple.WebCore                 0x000000010b85873b WTF::Detail::CallableWrapper<WebCore::MediaStreamTrackPrivate::sourceMutedChanged()::$_18, void, WebCore::MediaStreamTrackPrivate::Observer&>::call(WebCore::MediaStreamTrackPrivate::Observer&) + 11
1   com.apple.WebCore                 0x000000010b85536c WebCore::MediaStreamTrackPrivate::forEachObserver(WTF::Function<void (WebCore::MediaStreamTrackPrivate::Observer&)> const&) const + 652
2   com.apple.WebCore                 0x000000010b8559c9 WebCore::MediaStreamTrackPrivate::sourceMutedChanged() + 57
3   com.apple.WebCore                 0x000000010b859d4c WebCore::RealtimeMediaSource::forEachObserver(WTF::Function<void (WebCore::RealtimeMediaSource::Observer&)> const&) const + 652
4   com.apple.WebCore                 0x000000010b859a4b WebCore::RealtimeMediaSource::notifyMutedChange(bool) + 155
5   com.apple.WebCore                 0x000000010b8564c0 WebCore::RealtimeIncomingVideoSource::setSourceTrack(rtc::scoped_refptr<webrtc::VideoTrackInterface>&&) + 112
6   com.apple.WebCore                 0x000000010a235c08 WTF::Detail::CallableWrapper<WebCore::LibWebRTCMediaEndpoint::OnTrack(rtc::scoped_refptr<webrtc::RtpTransceiverInterface>)::$_13, void>::call() + 600
7   com.apple.JavaScriptCore          0x000000010d7585f9 WTF::dispatchFunctionsFromMainThread() + 361
8   com.apple.Foundation              0x00007fff4fe3a302 __NSThreadPerformPerform + 328
9   com.apple.CoreFoundation          0x00007fff4db5ede3 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
10  com.apple.CoreFoundation          0x00007fff4db5ed89 __CFRunLoopDoSource0 + 108
11  com.apple.CoreFoundation          0x00007fff4db4274b __CFRunLoopDoSources0 + 195
12  com.apple.CoreFoundation          0x00007fff4db41d15 __CFRunLoopRun + 1189
13  com.apple.CoreFoundation          0x00007fff4db4161e CFRunLoopRunSpecific + 455
14  com.apple.Foundation              0x00007fff4fda632f -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 280
15  com.apple.Foundation              0x00007fff4fda6204 -[NSRunLoop(NSRunLoop) run] + 76
16  libxpc.dylib                      0x00007fff79cd5077 _xpc_objc_main + 552
17  libxpc.dylib                      0x00007fff79cd4b79 xpc_main + 433
18  com.apple.WebKit                  0x0000000109183e53 WebKit::XPCServiceMain(int, char const**) + 547
19  libdyld.dylib                     0x00007fff79a9c3d5 start + 1

Platform

• OS: macOS
• Browser: Safari
• Browser Version: 13.0.3 (14608.3.10.10.1)
• Amazon Chime SDK GitHub Commit: dd65d7f