Several changes to component_build

Review URL: https://chromiumcodereview.appspot.com//12220088
web_ui changes for adding csslib to dwc.

-make CSS polyfill optional --css_polyfill
-minor cleanup
-Mutation problem
-Added CSS polyfill

Review URL: https://chromiumcodereview.appspot.com//12089095
Update to use latest source map

BUG=

Review URL: https://chromiumcodereview.appspot.com//12224102
Initial steps to add source map support in dwc:
 - Switches to use a new style of code printer that can track source map locations.
 - Changed to use new code printer: all the indentation done by hand, passing source-map location marks as we are emitting code.
 - source-map file is generated, but URLs are relative to base-dir. Once we start putting all the pieces together we can revisit this.

Review URL: https://chromiumcodereview.appspot.com//12221099
Fix up source map urls.

Review URL: https://chromiumcodereview.appspot.com//12217150
Adds support for Observable objects in web_ui.
This includes @observable annotation for automatic transformation by DWC. It also includes ObservableList/Map/Set types.

Observables use a batch-notification system where changes are queued up and sent to the handler during the "next microtask". This is similar to ES7 Object.observe proposal.

We don't have detailed change records yet but I plan to work on that in a follow up change. Keep that in mind when reviewing ObservableList/Map/Set types because they're in for an overhaul. The CL for that isn't ready but for comparison purposes you can find it here: https://chromiumcodereview.appspot.com/12096106/

All tests have been converted. Since I had to go through every single test, I took the liberty of removing incorrect <title> attributes throughout.

I still need to convert the MDV and explainer examples. I'm also interested in more perf tests. I'll work on that now, but would prefer not expanding the scope of this (already big) change :)

Feature request: https://github.com/dart-lang/web-ui/issues/259

Review URL: https://chromiumcodereview.appspot.com//12225039
Adds one-time final bindings.

Review URL: https://chromiumcodereview.appspot.com//12257024
template elements display:none in global stylesheet
This (roughly) matches the spec.

Review URL: https://chromiumcodereview.appspot.com//12212182
Ensure we don't add duplicate imports.

Review URL: https://chromiumcodereview.appspot.com//12253039
Add support for trimming and compacting text to help indent inside components.
To use this feature you must opt-in by adding an attribute to the template-tag
of a component (that's the only place where it is supported). See the test in
this CL for an example.

Review URL: https://chromiumcodereview.appspot.com//12207182
Generating appropriate source maps. This combines the power of edit-transactions
and code printers!

Review URL: https://chromiumcodereview.appspot.com//12271011
fixes for latest SDK, 0.3.6.2_r18539

* Url.isAbsolute() -> isAbsolute.
* API changes on Element
* remove some imports/exports were confusing analyzer

Review URL: https://chromiumcodereview.appspot.com//12260053
regenerate html setters

Review URL: https://chromiumcodereview.appspot.com//12207196
Fixes to get html offsets working also.

Review URL: https://chromiumcodereview.appspot.com//12256053
add @observable to editable_label and todo_row

todo_row doesn't strictly need it, but seems good practice since "todo" is using data binding.
I left it off router_options because it has no fields.

Review URL: https://chromiumcodereview.appspot.com//12212209
More fixes for the latest sdk. Just yesterday we got a few more breaking
changes in dart:html.

Review URL: https://chromiumcodereview.appspot.com//12290011
update version, fixes 366
Updates to webui for sdk 0.3.7+5

Review URL: https://chromiumcodereview.appspot.com//12288051
Update change log

Review URL: https://chromiumcodereview.appspot.com//12218170
fix typo ("Liscence" -> "Licence")