{
  "name": "Polymer Starter Kit",
  "short_name": "Polymer Starter Kit",
  "icons": [{
        "src": "images/touch/icon-128x128.png",
        "sizes": "128x128",
        "type": "image/png"
      }, {
        "src": "images/touch/apple-touch-icon.png",
        "sizes": "152x152",
        "type": "image/png"
      }, {
        "src": "images/touch/ms-touch-icon-144x144-precomposed.png",
        "sizes": "144x144",
        "type": "image/png"
      }, {
        "src": "images/touch/chrome-touch-icon-192x192.png",
        "sizes": "192x192",
        "type": "image/png"
      },{
        "src": "images/touch/chrome-splashscreen-icon-384x384.png",
        "sizes": "384x384",
        "type": "image/png"
      }],
  "start_url": "/?homescreen=1",
  "background_color": "#3E4EB8",
  "display": "standalone",
  "theme_color": "#2E3AA1"
}

{
  "name": "Polymer Starter Kit",
  "short_name": "Polymer Starter Kit",
  "icons": [{
        "src": "images/touch/icon-128x128.png",
        "sizes": "128x128",
        "type": "image/png"
      }, {
        "src": "images/touch/apple-touch-icon.png",
        "sizes": "152x152",
        "type": "image/png"
      }, {
        "src": "images/touch/ms-touch-icon-144x144-precomposed.png",
        "sizes": "144x144",
        "type": "image/png"
      }, {
        "src": "images/touch/chrome-touch-icon-192x192.png",
        "sizes": "192x192",
        "type": "image/png"
      },{
        "src": "images/touch/chrome-splashscreen-icon-384x384.png",
        "sizes": "384x384",
        "type": "image/png"
      }],
  "background_color": "#3E4EB8",
  "display": "standalone",
  "theme_color": "#2E3AA1"
}

Drop start_url - breaks routing/homescreen flow
Drop start_url - breaks routing/homescreen flow
