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freshen [tools]
modify tests to use mocha/chai from tools
CustomElements observation now handles olderShadowRoot's.
Ensure we have a __proto__ chain on platforms that don't natively support __proto__ (IE10).

This helps address https://github.com/Polymer/polymer/issues/217
Make native custom elements the default when it's supported.
Make native custom elements the default when it's supported.
make build work with native custom elements
temporarily make native document.register opt-in via ?register
Merge pull request #52 from Polymer/master

8/1 master -> stable