Google Fonts Without http Or https
A client recently upgraded his site to SSL, moving from http to https. Besides changing core constants like site URLs etc all external assets must also be served on https to prevent Mixed Content error.
This included Google Fonts. The preventive solution is to include them without any specific protocol like //fonts... instead of http://fonts... or https://fonts.
This will also save a little maintenance effort down the line when system is upgraded or downgraded.