Got this assertion when running `WebKit.MSEHasMediaStreamingActivity`

```
Running tests       
ASSERTION FAILED: Unhandled message RemoteSourceBufferProxy_SetTimestampOffset to 3
assertionFailureDueToUnreachableCode
/Users/jyavenard/Work/webkit/OpenSource/WebKitBuild/Debug/DerivedSources/WebKit/GPUConnectionToWebProcessMessageReceiver.cpp(133) : virtual void WebKit::GPUConnectionToWebProcess::didReceiveMessage(IPC::Connection &, IPC::Decoder &)
1   0x12facf388 WTFCrash
2   0x1149c17d8 WebKit::GPUConnectionToWebProcess::didReceiveMessage(IPC::Connection&, IPC::Decoder&)
3   0x116b93f24 IPC::Connection::dispatchMessage(IPC::Decoder&)
4   0x116b943e4 IPC::Connection::dispatchMessage(std::__1::unique_ptr<IPC::Decoder, std::__1::default_delete<IPC::Decoder>>)
5   0x116b94758 IPC::Connection::dispatchOneIncomingMessage()
6   0x116bb1d6c IPC::Connection::enqueueIncomingMessage(std::__1::unique_ptr<IPC::Decoder, std::__1::default_delete<IPC::Decoder>>)::$_17::operator()() const
7   0x116bb1cac WTF::Detail::CallableWrapper<IPC::Connection::enqueueIncomingMessage(std::__1::unique_ptr<IPC::Decoder, std::__1::default_delete<IPC::Decoder>>)::$_17, void>::call()
8   0x12faf7490 WTF::Function<void ()>::operator()() const
9   0x12fb903a4 WTF::RunLoop::performWork()
10  0x12fb94b9c WTF::RunLoop::performWork(void*)
11  0x19dc54f38 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
12  0x19dc54ecc __CFRunLoopDoSource0
13  0x19dc54c3c __CFRunLoopDoSources0
14  0x19dc53844 __CFRunLoopRun
15  0x19dc52db4 CFRunLoopRunSpecific
16  0x19ebc49cc -[NSRunLoop(NSRunLoop) runMode:beforeDate:]
17  0x19ec3d1ec -[NSRunLoop(NSRunLoop) run]
18  0x19d8c2424 _xpc_objc_main
19  0x19d8c1d44 xpc_main
20  0x114bc4b38 WebKit::XPCServiceMain(int, char const**)
21  0x116b648d4 WKXPCServiceMain
22  0x100fbff9c main
23  0x19d81bf34 start
LEAK: 1 WebProcessPool
LEAK: 1 WebPageProxy
worker/0 TestWebKitAPI.WebKit.MSEHasMediaStreamingActivity Passed
Ran 1 tests of 1 with 1 successful
```