generate_gradle.py currently builds & extracts all .srcjars as part of project generation. This is necessary so that studio's java analysis & refactoring steps can have access to the generated code.

However,
1) It's slow to build all srcjars for all targets, and
2) We now extract srcjars as part of building for codesearch's sake ( bug 890360 )

Since devs generally have targets that they care about already built, I think it's likely sufficient to instead just have project point to the extracted .jave files from 2).