Sync with 1644673
Sync with 1644673

Synced with angular/angular.io master branch, commit 1644673:
https://github.com/angular/angular.io/tree/1644673d6c9be60ec5e420b544cb3fa6a971d206/public/docs/_examples/attribute-directives/dart

googlearchive/attribute-directives,googlearchive/attribute-directives,angular-examples/attribute-directives,angular-examples/attribute-directives