Change the Chrome importer to emit schema-based markers

[mstange]

The Chrome importer currently creates markers whose data.type doesn't match a schema. Instead, we should have a schema and then set data.type to the name of the schema.

The data object also has other properties which need to be declared in a schema, for #5302.

In this example profile, most markers just have a category field. But some have a lot more data. You can find them by executing filteredMarkers.filter(m => m.data && Object.keys(m.data).length > 2) on the console.

I'm not sure what to do about that extra data. It could be stuffed in a field called chromeMarkerData with a new field format called freeform-object.

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