Use path based CSS classes instead of ID to style toolbar items individually (for icons)

In my code example, there is a mistake, the path of the second link is "/admin/content" too ;)
And the generated code once you applied the code should be :

[...]
<ul id="toolbar-menu"><li class="menu-15 path-admin-content-15 first"><a href="/admin/content" id="toolbar-link-admin-content-15" class="to-overlay"><span class="icon"></span>Content</a></li>
[...]
<li class="menu-126 path-admin-content-126"><a href="/admin/content" id="toolbar-link-admin-content-126" class="to-overlay"><span class="icon"></span>Find content</a></li>
[...]

mlid could vary depending on your installation, so the value of the CSS ID could not be exactly those for you, but they should be different between those two links.

About 1., Ok, it will be corrected in the follow-up(s).

About 2. Themeing those with a CSS class does not make more sense (to me at least), for example the menu items that made this "bug" apparent are in two different menus (a submenu of Mangement and Administration Shortcuts), cases where this would be useful are rare in my opinion because you'll change both menu item apparence.
To theme them, you'd usually use their parent CSS class and the HTML element as selector (as it is done in toolbar.css) to theme all the menu items, and in last resort (if you need to theme a particular menu item) use the menu item ID. If you need something more, you can always override theme functions.
I like the idea of path-based CSS ID, it makes it easier to maintain your CSS (toolbar-item-<mlid> would remove this concept), but they must be unique.
I'd like to hear more ideas about how this CSS could be generated so that it would be really unique, one which would not turn into something too big (i.e. not keeping a registry of all the CSS ID already used or similar gas factories) for this small task. Using the text of the link or the menu title is not realistic either, because you could have two items with the same text and path. This left me with the solution of the mlid, until now I always used this trick when theming with Drupal 6, but it ties the theme to one install usually, which is not a valid solution for core, so we should maybe drop the idea of unique ID in core and leave that to themers (or modules like menu_attributes) ?

Ok so mlid are not acceptable. And we require a way to theme shortcut individually to be able to assign them icons, but we cannot give unique CSS ID's reliably, so this is why I repurpose this issue and leave it up for grabs.

We discussed on IRC about it with Gábor Hojtsy and we decided that we should drop the current ID on the <a> and that themers could use the path based class of the <li>. For example to style the "Find content" shortcut, the CSS selector would be #toolbar-shortcuts li.path-admin-content. It removes the ID collisions and gives enough space to theme items individually. It should be noted that if there are two items with the same path in the same menu, the generated class will be the same for both, and it could cause problems for themers, in this edge case there is always the possibility for them to use theme override functions (menu) or contributed modules as mentioned before.

On this clean base of thoughts, the way the $link['href'] is cleaned to make CSS id/class is not reliable when there menu items point to an URL with a querystring or for external URL... so we should put some work in this at the same time.

Ok, this path does what I described in my previous message.
No more ID for the links, but they are themable individually with the class of their parent which is based on the path. The way used to clean the path has been changed and now should be exhaustive and always meet the CSS2 W3C recommandation for CSS identifiers. Tested it with :

• Relative URL (Internal Drupal paths) : admin/content generates path-admin-content
• Relative URL with querystring : admin/content?test1=val1&test2=val2 generates path-admin-content-test1-val1-test2-val2
• <front> special case : <front> generates path-front
• Absolute URL : http://www.example.com/ generates path-http-www-example-com
• Absolute URL with querystring : http://www.example.com/?test1=val1&test2=val2 generates path-http-www-example-com-test1-val1-test2-val2

Re-rolling... due to #326539: Convert 'class' attribute to use an array, not a string.

Marked #557492: duplicate id: toolbar-link-admin-content as duplicate.

Patch applies and tests pass locally.