System Menu disappears when using HighContrast themes

[YannUbuntu]

1. Open System Settings>Appearance
2. Change the theme to High Contrast.
3. Notice that the far right indicator, the system status menu, no longer has an icon. This makes it impossible for a typical user to log out of their account.

As a workaround, it's possible to click another menu, like the clock, and use the right arrow key to navigate to the basically invisible system menu.

This should be a high priority bug, as it makes the system less usable to those who have enabled an accessibility feature.

This will also affect the planned GNOME remix of Ubuntu as we use Adwaita by default but it will also include the Classic session with indicators. If 3D support doesn't work (such as in my VirtualBox testing today), the user will get the Classic session.

Original bug description
========================
On today's 12.04 daily ISO,

Steps to reproduce:
1. open up gnome-control-center
2. click appearance
3.change theme to "high contrast" or "high contrast inverse"
4. Look at the top right side of the menu bar : the System Menu has disappeared

[Omer Akram (om26er)]

that is not happening in Quantal. with unity 6.0

[Sebastien Bacher (seb128)]

See my comment on bug #1044148

"Thanks Jeremy, are you sure it happens in precise? It looks like bug #1018535 which I fixed in a SRU. It worked when I uploaded those packages for me but seems broken on quantal, I'm not sure why since the fix is still there.

The issue is basically that:
- the icon used is "system-devices-panel"
- the icon is not available in HighContrast theme
- gtk does fallbacking dropping the -<extra> as much as needed ... which goes down to "system"
- that icon is available in h-umanity-icon-theme

We made HighContrast fallback to Humanity is needed so it should use system.svg from there... it was working at the time I did the SRU, not sure what broke..."

[Jeremy Bícha (jbicha)]

And cross-posting my reply:

Seb, yes I just verified that it works like it's supposed to in Precise now; I'm surprised that it's not working in Quantal.

I thought I remembered reading it fixed in a changelog but couldn't find it when I was looking last night and didn't have a Precise install handy.

[Peter Hurley (phurley)]

This commit http://bazaar.launchpad.net/~indicator-applet-developers/indicator-session/trunk.12.10/revision/358
broke the "gtk does fallbacking dropping the -<extra> ... which goes down to system". Specifically;

  if (gtk_icon_theme_has_icon (indicator->icon_theme, icon) == FALSE)
    icon = "gtk-missing-image";

gtk_icon_theme_has_icon() does not provide the 'fallback' behavior expected (for obvious reasons).

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Balló György (ballogy)]

I created a more simpler patch that fixes the problem by using g_themed_icon_new_with_default_fallbacks () function to get the proper fallback names:
https://code.launchpad.net/~ballogy/indicator-session/better-fallback-icon/+merge/141608