Verify that navigator properly handles main frame navigated event.


Running: dumpInitialNavigator
top
  127.0.0.1:8000
    devtools/resources
      inspected-page.html

Running: attachFrame
top
  127.0.0.1:8000
    devtools/resources
      inspected-page.html
  frame (sourcemap-frame.html)
    127.0.0.1:8000
      devtools/bindings/resources
        sourcemap-frame.html
        sourcemap-script.js
        sourcemap-typescript.ts
        sourcemap-sass.scss
        sourcemap-style.css

Running: navigateMainFrame
top
  127.0.0.1:8000
    devtools/bindings/resources
      empty-page.html