Fix dart2js warning
Clean up whitespace
Merge pull request #3484 from keertip/tavern

rev up tavern version
Add default value for enable-polymer-designer to app.json
Merge remote-tracking branch 'upstream/master' into cde-polymer-designer
Merge pull request #3487 from ussuri/cde-polymer-designer

[Polymer Designer] Add default for flag + eliminate dart2js warning + whitespace/comments