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

third_party/polymer/v1_0/components-chromium/iron-collapse/iron-collapse-extracted.js

 Polymer({
 
     is: 'iron-collapse',
 
     behaviors: [
       Polymer.IronResizableBehavior
     ],
 
     properties: {
 
@@ skipping 31 matching lines @@
 
     },
 
     get dimension() {
       return this.horizontal ? 'width' : 'height';
     },
 
     /**
      * `maxWidth` or `maxHeight`.
      * @private
-     */    
+     */
     get _dimensionMax() {
       return this.horizontal ? 'maxWidth' : 'maxHeight';
     },
 
     /**
      * `max-width` or `max-height`.
      * @private
      */
     get _dimensionMaxCss() {
       return this.horizontal ? 'max-width' : 'max-height';
@@ skipping 28 matching lines @@
     },
 
     hide: function() {
       this.opened = false;
     },
 
     /**
      * Updates the size of the element.
      * @param {string} size The new value for `maxWidth`/`maxHeight` as css property value, usually `auto` or `0px`.
      * @param {boolean=} animated if `true` updates the size with an animation, otherwise without.
-     */     
+     */
     updateSize: function(size, animated) {
       // No change!
       var curSize = this.style[this._dimensionMax];
       if (curSize === size || (size === 'auto' && !curSize)) {
         return;
       }
 
       this._updateTransition(false);
       // If we can animate, must do some prep work.
       if (animated && !this.noAnimation && this._isDisplayed) {
         // Animation will start at the current size.
         var startSize = this._calcSize();
         // For `auto` we must calculate what is the final size for the animation.
         // After the transition is done, _transitionEnd will set the size back to `auto`.
         if (size === 'auto') {
           this.style[this._dimensionMax] = '';
           size = this._calcSize();
         }
         // Go to startSize without animation.
         this.style[this._dimensionMax] = startSize;
-        // Force layout to ensure transition will go. Set offsetHeight to itself
+        // Force layout to ensure transition will go. Set scrollTop to itself
         // so that compilers won't remove it.
-        this.offsetHeight = this.offsetHeight;
+        this.scrollTop = this.scrollTop;
         // Enable animation.
         this._updateTransition(true);
       }
       // Set the final size.
       if (size === 'auto') {
         this.style[this._dimensionMax] = '';
       } else {
         this.style[this._dimensionMax] = size;
       }
     },
@@ skipping 59 matching lines @@
         if (rect[prop] !== 0) return true;
       }
       return false;
     },
 
     _calcSize: function() {
       return this.getBoundingClientRect()[this.dimension] + 'px';
     }
 
   });