Observe nodes

[cdata]

This change does the following:

• Removes a temporary patch obsoleted by https://github.com/Polymer/polymer/issues/2535
• Replaces usage of MutationObserver with Polymer.dom(...).observeNodes

/cc @notwaldorf

This branch is blocked by https://github.com/Polymer/polymer/pull/2548 being tagged. It is currently released on polymer#master, but until it is tagged these changes cannot be merged into iron-selected#master.

[cdata]

/cc @azakus

[sorvell]

Can we add a test that would have failed before? For example, add a node that only gets to distributed to a child of the selector via re-projection?

[sorvell]

Why don't we change the items property so that it's only calculated when we get a signal that the items may have changed (startup + when observedNodes tells you).

[cdata]

Feedback addressed. Tests are failing locally due to a bug in observeNodes, reported offline to @sorvell

[cdata]

Also, I threw in a fix for #69 since it was relevant and it felt lame to fix it with the old code.

[cdata]

add a node that only gets to distributed to a child of the selector via re-projection?

We already appear to have tests for this that passed. See: https://github.com/PolymerElements/iron-selector/blob/master/test/content.html

Hrm..

[cdata]

Already resolved, but this change now depends on resolution of https://github.com/Polymer/polymer/issues/2587

[notwaldorf]

Just a note for future @cdata: You'll need to bump the Polymer version up in bower.json to 1.2.0