[ts] Typecheck source_frame/XMLView.js with TypeScript
[ts] Typecheck source_frame/XMLView.js with TypeScript

Bug: chromium:1011811
Change-Id: I2ef30c7d2f4aea6700b01306acd38f65fcae2a06
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2505507
Commit-Queue: Andres Olivares <9d3bededfc9b98cb289557338a8f98e77d597607@chromium.org>
Reviewed-by: Paul Lewis <8915f5d5c39a08c5a3e8a8d7314756e4580816f9@chromium.org>

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