Web updates

HTML a3df3e9e40fa

Always replace the initial about:blank Document Previously, the caller of the navigate algorithm would (usually) check for the browsing context still being on the initial about:blank Document, and if so, switch its history handling to "replace". However, a few call sites missed this: e.g., following hyperlinks or when they were targeted at an existing browsing context. This change instead centralizes the conversion of "default" navigations into "replace" navigations for the initial about:blank Document. This also fixes a minor bug where the conversion of "default" into "replace" navigations for same-URL fragment navigations was not taking place correctly, due to the check being located after the fragment navigation step. Closes #6491.

Domenic Denicola