[DevTools] Keep IP address of HttpServer as a member of DevToolsHttpHandlerImpl.
Fix the problem that loading inspector from content_shell is failing with
thread_checker_.CalledOnValidThread() failed.
At ShellDevToolsFrontend::Show(), DevToolsHttpHandlerImpl::GetFrontendURL()
is called to get the frontend url, and inside the function,
HttpServer::GetLocalAddress() is called directly which is expected to be
called on the DevToolsHandler thread only.
To prevent the DCHECK failure, this patch keeps the ip address of HttpServer
as a member of DevToolsHttpHandlerImpl instance and use it.
BUG=425423
Review URL: https://codereview.chromium.org/
666673007
Cr-Commit-Position: refs/heads/master@{#301684}