Called when a content shell is added to the docshell tree. This is
only called for “root” content shells (that is, ones whose parent is a
chrome shell).
| aContentShell | the shell being added. |
| aPrimary | whether the shell is primary. |
| aTargetable | whether the shell can be a target for named window targeting. |
| aID | the "id" of the shell. What this actually means is undefined. Don't rely on this for anything. |
Called when a content shell is removed from the docshell tree. This is
only called for “root” content shells (that is, ones whose parent is a
chrome shell). Note that if aContentShell was never added,
contentShellRemoved should just do nothing.
| aContentShell | the shell being removed. |