Due to applying closure compiler to all js files even when only a dependency is changed.

Example build trace
https://chromium-build-stats.appspot.com/ninja_log/2018/09/05/swarm1801-c4/ninja_log.swarm1801-c4.chrome-bot.20180904-190801.3410.gz/trace.html from https://ci.chromium.org/p/chromium/builders/luci.chromium.try/android-kitkat-arm-rel/74133

I think it is better to extract closure compile step from grit to utilize build incrementability.