[DevTools] Network: test that reported html-metohd is correct.

See fix: https://codereview.chromium.org/22826002/

BUG=270683

Review URL: https://chromiumcodereview.appspot.com/22953003

git-svn-id: svn://svn.chromium.org/blink/trunk@158535 bbb929c8-8fbe-4397-9dbb-9b2b20218538