Capture # of connections opened per domain

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After more discussion in catchpoint/WebPageTest.tsproxy#9 about failures. I was thinking we could capture total opened connection id counts per domain for analysis which could be beneficial. I know we can get this from the chrome logs not sure about firefox. We could possible use this to let a user know in coach that they are opening a lot of new connections and the load of a site could be affected by TCP slow start. They should reduce those to help with speeding up their page resources.