Cleaning up the perf Gruntfile.

First is a series of steps, the long term goal is outlined in design.md.

This CL simplifies the Grunt file.

It also makes the debug build much better, so that a debug build has non-minified JS and fully expanded web components (core-* and paper-*).

Uses bower to get all dependencies, where before the Promise polyfill was pulled in via npm.

This also moves perf/res/js/common.js into /res/js/common.js so that everyone can use in from there.

BUG=skia:

Review URL: https://codereview.chromium.org/748873002