Roll Polymer from 1.5.0 -> 1.6.0 to pick up native CSS custom props

third_party/polymer/v1_0/components-chromium/iron-autogrow-textarea/bower.json

 {
   "name": "iron-autogrow-textarea",
-  "version": "1.0.12",
+  "version": "1.0.13",
   "description": "A textarea element that automatically grows with input",
   "authors": [
     "The Polymer Authors"
   ],
   "keywords": [
     "web-components",
     "polymer",
     "input",
     "textarea"
   ],
   "main": "iron-autogrow-textarea.html",
   "private": true,
   "repository": {
     "type": "git",
     "url": "git://github.com/PolymerElements/iron-autogrow-textarea.git"
   },
   "license": "http://polymer.github.io/LICENSE.txt",
   "homepage": "https://github.com/PolymerElements/iron-autogrow-textarea",
   "ignore": [],
   "dependencies": {
     "iron-behaviors": "PolymerElements/iron-behaviors#^1.0.0",
     "iron-flex-layout": "PolymerElements/iron-flex-layout#^1.0.0",
     "iron-validatable-behavior": "PolymerElements/iron-validatable-behavior#^1.0.0",
     "iron-form-element-behavior": "PolymerElements/iron-form-element-behavior#^1.0.0",
-    "polymer": "Polymer/polymer#^1.0.0"
+    "polymer": "Polymer/polymer#^1.1.0"
   },
   "devDependencies": {
     "iron-component-page": "PolymerElements/iron-component-page#^1.0.0",
     "iron-demo-helpers": "PolymerElements/iron-demo-helpers#^1.0.0",
     "iron-test-helpers": "PolymerElements/iron-test-helpers#^1.0.0",
     "test-fixture": "PolymerElements/test-fixture#^1.0.0",
     "web-component-tester": "^4.0.0",
     "paper-styles": "PolymerElements/paper-styles#^1.0.0",
     "webcomponentsjs": "webcomponents/webcomponentsjs#^0.7.0"
   }
 }