This commit allows to log tofu detection always,
even if the rest of the webfonts library is not loaded.
By default this is disabled.
To enable it, set the variable $wgULSTofuLoggingChance
to a number between 0 and 100, indicating the chance of it
getting logged. The idea of the lottery is that even a partial
sample can be useful.
Change-Id: Ia08fe0de348b7eebfa95498a6be58ae41608ba3b
10a25c1cc9