Trace visibility improvements.

Screencast: https://screencast.googleplex.com/cast/NDk5OTYzODAyODM4NjMwNHw3Y2JmMjRiZS1hMQ

Indicate whether trace is a dump in the tab title, and in the entry of hierarchy tree if timestamp not available.
Provide file name on hover.
Also fixed bug with trying to access undefined hierarchy trees, noticed from the traces in b/350658276.

Fixes: 350658276
Fixes: 342561886
Test: npm run test:unit:ci
Change-Id: If1c9cf1435e45a4e5feb765d8469c73fb712b472
26 files changed