From: 
Half-Life 2: Awakening
"GameInfo"
{
game "Awakening"
icon logo
type "singleplayer_only"
developer "Bluestrike"
developer_url "http://www.bluestrike.be"
FileSystem
{
SteamAppId 215 // This will mount all the GCFs we need (240=CS:S, 220=HL2).
ToolsAppId 211 // Tools will load this (ie: source SDK caches) to get things like materials\debug, materials\editor, etc.
SearchPaths
{
Game |gameinfo_path|.
Game sourcetest
Game hl2
}
}
}