Improve UX when the timeline events for a frame are not available

Sometimes, selecting a frame in the Frames chart that doesn't have Timeline Events shows a toast in the bottom right:

Steps to reproduce:
1. Run an app in profile mode and connect to DevTools
2. Trigger some frames
3. Refresh the DevTools web application
4. Select a frame that was gathered before the refresh
5. See toast message

Instead, I would like some indication where the Timeline Events chart is displayed that tells me there are no timeline events for this frame, and that I should trigger some new frames and maybe avoid refreshing the page. Right now the Timeline Events chart will either show no frame data or the frame data for the previous frame that was selected. Instead, maybe this could be greyed out to indicate that there's a problem.

通过 Frames chart 重现该问题，并检查在选择刷新前收集的 frame 后 Timeline Events chart 的响应情况。当图表区域指示时间线事件不可用，而不是显示过时数据或仅显示 toast，并提供触发新 frame 且避免刷新的指导时，工作即完成。

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