cleanup(build): remove traceur-based Dart transpiler

Author: alexeagle

tools/transpiler/spec/for_of_spec.js

@@ -71,10 +71,7 @@ export function main() {
 
  expect(function() {
  wf.name = true;
- }).toThrowError(IS_DARTIUM ?
- // Dart
- "type 'bool' is not a subtype of type 'String' of 'value'" :
- // JavaScript
+ }).toThrowError(
  // TODO(vojta): Better error, it's not first argument, it's setting a field.
  'Invalid arguments given!\n' +
  ' - 1st argument has to be an instance of string, got true'
@@ -86,10 +83,7 @@ export function main() {
  it('should fail when setting wrong type value', function() {
  expect(function() {
  WithFields.id = true;
- }).toThrowError(IS_DARTIUM ?
- // Dart
- "type 'bool' is not a subtype of type 'num' of 'id'" :
- // JavaScript
+ }).toThrowError(
  // TODO(vojta): Better error, it's not first argument, it's setting a field.
  'Invalid arguments given!\n' +
  ' - 1st argument has to be an instance of number, got true'