Dart polymer: style bindings do not compile to JS

[DartBot]

This issue was originally filed by yurir...@gmail.com

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What steps will reproduce the problem?

1. Take custom_element_with_style project
   https://github.com/sethladd/dart-polymer-dart-examples/blob/master/web/custom_element_with_style/index.html
2. In html file replace
                   #message {
                       color: pink;
                   }
   with
                   #message {
                       color: {{color}};
                   }
3. in Dart file add
     @­observable
     String color = "pink";
   to MyElement class
4. Create build file:
   import 'dart:io';
   import 'package:polymer/component_build.dart';
   main() {
     build(new Options().arguments, ['web/custom_element_with_style/index.html']);
   }
5. Run the build file

What is the expected output? What do you see instead?
Expected: no errors. Generated java script code works like dart code
 Actual:
warning :17:29: expected }, but found {
                    color: {{color}};
                            ^
warning :17:35: expected :, but found }
                    color: {{color}};
                                  ^
warning :17:37: premature end of file unknown CSS
                    color: {{color}};

What version of the product are you using? On what operating system?
  polymer:
    description: polymer
    source: hosted
    version: "0.7.2+1"

Please provide any additional information below.

[dgrove]

cc @terrylucas.
Added Area-Polymer, Triaged labels.

[jmesserly]

style bindings cannot work under polyfill, see
Polymer/polymer#270

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Added MovedToGithub label.

[sigmundch]

Issue #15776 has been merged into this issue.