Roll third_party/polymer.

third_party/polymer/v1_0/components-chromium/iron-scroll-target-behavior/iron-scroll-target-behavior-extracted.js

Index: third_party/polymer/v1_0/components-chromium/iron-scroll-target-behavior/iron-scroll-target-behavior-extracted.js
diff --git a/third_party/polymer/v1_0/components-chromium/iron-scroll-target-behavior/iron-scroll-target-behavior-extracted.js b/third_party/polymer/v1_0/components-chromium/iron-scroll-target-behavior/iron-scroll-target-behavior-extracted.js
index 6ab3521e82241216d1408d317b9cdad7f1c22053..7e3f09a8f160f9f4992ad66959c07764330daa32 100644
--- a/third_party/polymer/v1_0/components-chromium/iron-scroll-target-behavior/iron-scroll-target-behavior-extracted.js
+++ b/third_party/polymer/v1_0/components-chromium/iron-scroll-target-behavior/iron-scroll-target-behavior-extracted.js
@@ -15,20 +15,31 @@
 
       /**
        * Specifies the element that will handle the scroll event
-       * on the behalf of the current element. This is typically a reference to an `Element`,
+       * on the behalf of the current element. This is typically a reference to an element,
        * but there are a few more posibilities:
        *
        * ### Elements id
        *
        *```html
-       * <div id="scrollable-element" style="overflow-y: auto;">
+       * <div id="scrollable-element" style="overflow: auto;">
        *  <x-element scroll-target="scrollable-element">
-       *    Content
+       *    <!-- Content-->
        *  </x-element>
        * </div>
        *```
-       * In this case, `scrollTarget` will point to the outer div element. Alternatively,
-       * you can set the property programatically:
+       * In this case, the `scrollTarget` will point to the outer div element. 
+       *
+       * ### Document scrolling
+       *
+       * For document scrolling, you can use the reserved word `document`:
+       *
+       *```html
+       * <x-element scroll-target="document">
+       *   <!-- Content -->
+       * </x-element>
+       *```
+       *
+       * ### Elements reference
        *
        *```js
        * appHeader.scrollTarget = document.querySelector('#scrollable-element');
@@ -49,42 +60,39 @@
     ],
 
     _scrollTargetChanged: function(scrollTarget, isAttached) {
-      // Remove lister to the current scroll target
+      var eventTarget;
+
       if (this._oldScrollTarget) {
-        if (this._oldScrollTarget === this._doc) {
-          window.removeEventListener('scroll', this._boundScrollHandler);
-        } else if (this._oldScrollTarget.removeEventListener) {
-          this._oldScrollTarget.removeEventListener('scroll', this._boundScrollHandler);
-        }
+        eventTarget = this._oldScrollTarget === this._doc ? window : this._oldScrollTarget;
+        eventTarget.removeEventListener('scroll', this._boundScrollHandler);
         this._oldScrollTarget = null;
       }
-      if (isAttached) {
-        // Support element id references
-        if (typeof scrollTarget === 'string') {
-
-          var host = this.domHost;
-          this.scrollTarget = host && host.$ ? host.$[scrollTarget] : 
-              Polymer.dom(this.ownerDocument).querySelector('#' + scrollTarget);
-
-        } else if (this._scrollHandler) {
-
-          this._boundScrollHandler = this._boundScrollHandler || this._scrollHandler.bind(this);
-          // Add a new listener
-          if (scrollTarget === this._doc) {
-            window.addEventListener('scroll', this._boundScrollHandler);
-            if (this._scrollTop !== 0 || this._scrollLeft !== 0) {
-              this._scrollHandler();
-            }
-          } else if (scrollTarget && scrollTarget.addEventListener) {
-            scrollTarget.addEventListener('scroll', this._boundScrollHandler);
-          }
-          this._oldScrollTarget = scrollTarget;
-        }
+
+      if (!isAttached) {
+        return;
+      }
+      // Support element id references
+      if (scrollTarget === 'document') {
+
+        this.scrollTarget = this._doc;
+
+      } else if (typeof scrollTarget === 'string') {
+
+        this.scrollTarget = this.domHost ? this.domHost.$[scrollTarget] :
+            Polymer.dom(this.ownerDocument).querySelector('#' + scrollTarget);
+
+      } else if (this._isValidScrollTarget()) {
+
+        eventTarget = scrollTarget === this._doc ? window : scrollTarget;
+        this._boundScrollHandler = this._boundScrollHandler || this._scrollHandler.bind(this);
+        this._oldScrollTarget = scrollTarget;
+
+        eventTarget.addEventListener('scroll', this._boundScrollHandler);
       }
     },
 
     /**
-     * Runs on every scroll event. Consumer of this behavior may want to override this method.
+     * Runs on every scroll event. Consumer of this behavior may override this method.
      *
      * @protected
      */