[ts] Typecheck css_overview/CSSOverviewCompletedView.js with TypeScript
[ts] Typecheck css_overview/CSSOverviewCompletedView.js with TypeScript

Bug: chromium:1011811
Change-Id: I15140b5ada12ca6085fdf0a725c8d131dbce4498
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2406193
Commit-Queue: Andres Olivares <9d3bededfc9b98cb289557338a8f98e77d597607@chromium.org>
Reviewed-by: Tim van der Lippe <dba8716ee7f8d16236046f74d2167cb94410f6ed@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend