third_party/instrumented_libraries has code to download instrumented libraries, and to build new versions of those. Only the first part is currently part of the gn build.

We don't build new instrumented libraries super often so we could use the gyp files to build new libraries, but that means we'll have to keep build/common.gypi around since it depends on that.

So here's a bug for porting that part to gn as well.