Remove unused code and fix some stylistic issues.
Really basic coverage support for test-runner
Remove parent argument from TimedItem constructors
Add and use a utility for abstract methods
Remove dead code
Fix *Group.clear
Merge pull request #231 from web-animations/coverage

Really basic coverage support for test-runner
Merge pull request #232 from dstockwell/dead-code

Remove parent arguments and dead code. Simplify abstract methods.
Merge pull request #221 from dstockwell/clean-up-testharness

Remove unused code and fix some stylistic issues in testharness_extetensions/timing
Merge branch 'master' of https://github.com/web-animations/web-animations-js