DevTools performance page broken when using systrace recorder

When launching an app with `--trace-systrace`, the performance tab in DevTools just spins, and JS console shows the following:

@bkonyi is there a way for us to check at runtime which timeline recorder is being used? If the systrace recorder is in use, in DevTools we should gate our logic that depends on timeline events from the VM service and we should provide the user with instructions on how to load this trace into DevTools from file or into ui.perfetto.dev directly.

从 DevTools 的性能标签页处理来自 VM service 的时间线事件入手，调查在使用 --trace-systrace 时如何在运行时识别活动的时间线记录器。完成标准是：对于 systrace 跟踪，页面不再持续转圈，并且用户会收到从文件或在 ui.perfetto.dev 中加载跟踪的说明。

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