I'm surprised Facebook and all its peripheral development has that much source. I would expect something like 5-10 million lines of code, not ~100 million lines implied by the example.
It is useful to keep in mind that Facebook isn't just the front-end (and isn't just code, also images, configuration, and so forth).
Just talking about open source stuff, Facebook also generates code like Cassandra, Hive (data warehousing application), Phabricator (a code review and lifecycle tool), HipHop for PHP (the translator/compiler, the interpreter, and the virtual machine), FlashCache (a kernel driver), Thrift, Scribe, and so forth.
We also have had to build applications to support our operations, so think about what sort of effort goes into building scalable monitoring, configuration management, automatic remediation, logging infrastructure, and so forth.
I don't know the actual lines of code across it all, and wouldn't mention it if I did, but people often underestimate the scale here.