Final polish for `asyncWork` branch.
Final polish for `asyncWork` branch.

Polymer/tools,rcorp/vulcanize,Polymer/tools,Polymer/tools,Polymer/polymer-bundler,Polymer/tools,bendroid/vulcanize,bendroid/vulcanize,rcorp/vulcanize,Polymer/polymer-bundler,Polymer/polymer-bundler,threeday0905/vulcanize,threeday0905/vulcanize