1424079 - Convert _maybeToggleBookmarkToolbarVisibility to use async Places APIs

Status: NEW

(Firefox :: Migration, enhancement, P3)

Description

[Matthew N. [:MattN]]

In bug 1415692, code was brought back to show the bookmarks toolbar for new/reset profiles if there are a certain number of bookmarks imported/restored to the user's bookmark toolbar.

:mak would like the Places API usage to be converted to use async APIs. That wasn't done in bug 1415692 since the code needs to run before the first window shows (to get the toolbar state correct) and fixing that would add more risk for uplift.

Two possible approaches:
a) make the migrateUI method async and have it wait for the Places API usage.
** This won't cause any UI flicker as the toolbar will be toggled before the window opens still.
b) Let the calculation of bookmark toolbar items be async but broadcast to all windows to show the bookmark toolbar if required in open windows. See the "autoshow-bookmarks-toolbar" (I could have sworn there was another that also showed the toolbar but I could be mistaken).

Relevant code: https://hg.mozilla.org/mozilla-central/diff/49358c06a122/browser/components/nsBrowserGlue.js