Closure Compiler is made to be used with Closure Library to assemble
"JavaScript binaries" that are compressed JavaScript files that
include both your files and what you pull from Closure Library.
So while there's not an AJAX API to pull Closure Library, there's a
Closure Compiler webservice that you can use to generate the compiled
JavaScript for your project. That's located here:
http://closure-compiler.appspot.com/home
You can also use the compiler locally. See the documentation for tips on that.
Thanks,
Nathan