fix build -- observable_test was not updated to the right import

Review URL: https://chromiumcodereview.appspot.com//13470025
Small change: remove a boolean property that can be derived

Review URL: https://chromiumcodereview.appspot.com//13465020
fix emitter_test to construct valid trees

Review URL: https://chromiumcodereview.appspot.com//13464017
Add support for id bindings
Fairly straightforward, the only tricky issue is that we maniuplate the DOM structure.
Note: this builds on my earlier change to make emitter_test test valid trees.

Review URL: https://chromiumcodereview.appspot.com//13474010
fix #399 - remove EqualityTest

Review URL: https://chromiumcodereview.appspot.com//13460019
fix #390 - test web_ui root build.dart

Review URL: https://chromiumcodereview.appspot.com//13493003
Fix #82 - use the native DOM node type that we are extending.
In practice, it means `<x-foo>` becomes `<base-tag is="x-foo">`.

Pros:
* extends tag now does something
* custom tags render correctly and host node has the right APIs
* makes our custom-tags less leaky

Cons:
* Query and CSS selectors become more leaky, need to use base-tag[is=custom-tag]

(where "leaky" means "leaky abstraction")

Review URL: https://chromiumcodereview.appspot.com//13607004
Use KeyEvent... it's just better
This is a partial fix for #357.

Review URL: https://chromiumcodereview.appspot.com//13540005
merged
Move to another branch