With this patch, we now initialize the `WebContentConsoleClient` as soon
as the Page has loaded, instead of waiting for the Console Window to be
shown. This finally lets us see log messages that happened before the
window was opened! :^)
However, it is not perfect. Waiting until the page has loaded means we
lose any messages that happen *during* page load. Ideally we would
initialize the WCCC when the page *starts* loading instead, but it
requires that the page has a document and interpreter assigned and
accessible. As far as I can tell with my limited knowledge, this is not
the case until the page has completed loading.
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