There are 3 issues here:
- the runtime changing of the title causes issues where the content title is
not set. This is fixed by setting it to the private title by default;
there is very little (if any) UI that allows users to even open
about:privatebrowsing in 'normal' windows so we care a lot less about
flicker there. To be able to include this title in the markup, we switched
to a dtd.
- the 'empty tab' title we set on the tab initially is set when the tab is
created. This has been updated to check for private windows, and default to
'Private Browsing' instead. This will obviously also affect other new tabs
in private browsing, but that seems desirable/consistent.
- Likewise, we use this title when updating a tab's title that we don't yet
have a content title for (which can still happen while about:privatebrowsing
is loading because e10s), and so that is updated, too.
MozReview-Commit-ID: nVfXD2M6UZ
97c3b183c4