valve: Add trimmed traces from some Valve games.

I got an ack from @Plagman to include Valve titles in traces-db.
These come from the traces that Chrome OS uses, trimmed by me to be
shorter (just get to an interesting frame in the game), and repacked
to brotli level 11 to save disk space.

CS: 17MB
CS Source: 71MB
HL2: 102MB
Portal 2: 223MB