566226 - Add pref to disable native themes in Web content

Status: NEW

(Core :: Widget, defect)

Description

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Currently GTK has its own specific pref to disable native themes globally (see gDisableNativeTheme). We should extend this so that a) we can disable native themes in Web content but leave them enabled for chrome and b) this pref works on all platforms. This will help us measure the performance impact of native theming and give distributors more options.

I'd add a new boolean pref "mozilla.widget.disable-native-theme-content" to disable themes just in content. Then I'd modify nsPresContext::GetTheme to have two cached themes, one for chrome and one for content, and choose the right theme based on IsChrome(). I'd also modify nsBox to get the theme from the prescontext:
http://mxr.mozilla.org/mozilla-central/source/layout/xul/base/src/nsBox.cpp#221

Karl, maybe you could do this? It should be quick.

Comment 1

[Karl Tomlinson (:karlt)]

Noting that the proposed implementation here differs from that suggested in bug 563886 comment 3.

Comment 2

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

This probably makes more sense, since it means less duplicated code between widget implementations.  (Do we want to move the existing pref into nsPresContext at the same time, rather than have it implemented separately in each widget implementation?)

Comment 3

[Karl Tomlinson (:karlt)]

Having the two prefs together in nsPresContext looks like it would make sense.