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

third_party/polymer/v1_0/components-chromium/paper-ripple/bower.json

 {
   "name": "paper-ripple",
-  "version": "1.0.7",
+  "version": "1.0.8",
   "license": "http://polymer.github.io/LICENSE.txt",
   "description": "Adds a material design ripple to any container",
   "private": true,
   "authors": [
     "The Polymer Authors"
   ],
   "keywords": [
     "web-components",
     "polymer",
     "ripple"
   ],
   "repository": {
     "type": "git",
     "url": "git://github.com/PolymerElements/paper-ripple.git"
   },
   "main": "paper-ripple.html",
   "dependencies": {
-    "iron-a11y-keys-behavior": "polymerelements/iron-a11y-keys-behavior#^1.1.4",
+    "iron-a11y-keys-behavior": "polymerelements/iron-a11y-keys-behavior#^1.1.5",
     "polymer": "Polymer/polymer#^1.1.0"
   },
   "devDependencies": {
     "iron-component-page": "polymerelements/iron-component-page#^1.0.0",
     "iron-icon": "polymerelements/iron-icon#^1.0.0",
     "iron-icons": "polymerelements/iron-icons#^1.0.0",
     "iron-test-helpers": "PolymerElements/iron-test-helpers#^1.0.0",
     "paper-styles": "polymerelements/paper-styles#^1.0.0",
     "test-fixture": "polymerelements/test-fixture#^1.0.0",
     "web-component-tester": "^4.0.0",
     "webcomponentsjs": "webcomponents/webcomponentsjs#^0.7.0"
   },
   "ignore": []
 }