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

third_party/polymer/v1_0/components-chromium/paper-behaviors/paper-button-behavior-extracted.js

 /** @polymerBehavior Polymer.PaperButtonBehavior */
   Polymer.PaperButtonBehaviorImpl = {
-
     properties: {
-
       /**
        * The z-depth of this element, from 0-5. Setting to 0 will remove the
        * shadow, and each increasing number greater than 0 will be "deeper"
        * than the last.
        *
        * @attribute elevation
        * @type number
        * @default 1
        */
       elevation: {
         type: Number,
         reflectToAttribute: true,
         readOnly: true
       }
-
     },
 
     observers: [
       '_calculateElevation(focused, disabled, active, pressed, receivedFocusFromKeyboard)',
       '_computeKeyboardClass(receivedFocusFromKeyboard)'
     ],
 
     hostAttributes: {
       role: 'button',
       tabindex: '0',
@@ skipping 35 matching lines @@
      * create a ripple up effect.
      *
      * @param {!KeyboardEvent} event .
      */
     _spaceKeyUpHandler: function(event) {
       Polymer.IronButtonStateImpl._spaceKeyUpHandler.call(this, event);
       if (this.hasRipple()) {
         this._ripple.uiUpAction();
       }
     }
-
   };
 
   /** @polymerBehavior */
   Polymer.PaperButtonBehavior = [
     Polymer.IronButtonState,
     Polymer.IronControlState,
     Polymer.PaperRippleBehavior,
     Polymer.PaperButtonBehaviorImpl
   ];