Fixes in web_ui for the next sdk

Review URL: https://chromiumcodereview.appspot.com//12093025
Fixes from code review

Review URL: https://chromiumcodereview.appspot.com//12084039
Style attributes and printing messages:
* Move the map support from data-style to style.
* Make messages print again (I noticed that we were again not printing things
  now that I added a new warning).

Review URL: https://chromiumcodereview.appspot.com//11717002
Support for constant attributes passed to web components

Review URL: https://chromiumcodereview.appspot.com//11708002