Buck: Set up Closure Compiler tool chain to minify JavaScript code

Extend the build tool chain to minify JavaScript from CodeMirror
distribution.

Currently SIMPLE_OPTIMIZATIONS mode is used, as ADVANCED_OPTIMIZATIONS
doesn't seem to work.  But even with simple mode the minification factor
is:

393441:cm3-verbose.js
167971:cm3_minified.js

And even more for language modes:

56029:perl-verbose.js
10122:perl-minified.js

Disadvantage: Longer compilation time. In follow-up changes we may want
to optimize it by disabling JS minification in development build.

Change-Id: I24790e84484add4f02b3821cca4b69e62fde0c22
2 files changed