1442601 - Refactor ext-devtools-panels.js to reuse more helpers coming from the webext-panels.xul used by extension sidebar pages

Status: NEW

(WebExtensions :: Developer Tools, enhancement, P3)

Description

[Luca Greco [:rpl] [:luca] [:lgreco]]

This issue is a follow up of Bug 1417043, which re-use the webext-panels.xul document (and the related webext-panels.js script) in ext-devtools-panels.js, to share some of the fixes related to the extensions running in oop mode (in particular related to the select and autocompletion dropdowns). 

In Bug 1417043 ext-devtools-panels.js is still going to create and manage the browser XUL elements where the devtools panels are loaded (because of some difference in the lifecycle and particular issues related to the devtools panels vs. the browser sidebars, as described in a bit more detail in Bug 1417043 comment 9).

The goal of this issue is to refactor webext-panels.xul/webext-panels.js and ext-devtools-panels.js so that we create the XUL browser elements using the helper defined in webext-panels.js (instead of just reusing the XUL page where the XUL browser elements are inserted).