Rolling forward https://codereview.chromium.org/1155683008/ which was

third_party/polymer/v0_8/components-chromium/iron-resizable-behavior/iron-resizable-behavior-extracted.js

-
-  /**
-   * `IronResizableBehavior` is a behavior that can be used in Polymer elements to
-   * coordinate the flow of resize events between "resizers" (elements that control the
-   * size or hidden state of their children) and "resizables" (elements that need to be
-   * notified when they are resized or un-hidden by their parents in order to take
-   * action on their new measurements).
-   * Elements that perform measurement should add the `IronResizableBehavior` behavior to
-   * their element definition and listen for the `iron-resize` event on themselves.
-   * This event will be fired when they become showing after having been hidden,
-   * when they are resized explicitly by another resizable, or when the window has been
-   * resized.
-   * Note, the `iron-resize` event is non-bubbling.
-   *
-   * @polymerBehavior Polymer.IronResizableBehavior
-   * @demo demo/index.html
-   **/
-  Polymer.IronResizableBehavior = {
-    properties: {
-      _parentResizable: {
-        type: Object,
-        observer: '_parentResizableChanged'
-      }
-    },
-
-    listeners: {
-      'iron-request-resize-notifications': '_onIronRequestResizeNotifications'
-    },
-
-    created: function() {
-      // We don't really need property effects on these, and also we want them
-      // to be created before the `_parentResizable` observer fires:
-      this._interestedResizables = [];
-      this._boundNotifyResize = this.notifyResize.bind(this);
-    },
-
-    attached: function() {
-      this.fire('iron-request-resize-notifications', null, {
-        node: this,
-        bubbles: true
-      });
-
-      if (!this._parentResizable) {
-        window.addEventListener('resize', this._boundNotifyResize);
-        this.notifyResize();
-      }
-    },
-
-    detached: function() {
-      if (this._parentResizable) {
-        this._parentResizable.stopResizeNotificationsFor(this);
-      } else {
-        window.removeEventListener('resize', this._boundNotifyResize);
-      }
-
-      this._parentResizable = null;
-    },
-
-    /**
-     * Can be called to manually notify a resizable and its descendant
-     * resizables of a resize change.
-     */
-    notifyResize: function() {
-      if (!this.isAttached) {
-        return;
-      }
-
-      this._interestedResizables.forEach(function(resizable) {
-        // TODO(cdata): Currently behaviors cannot define "abstract" methods..
-        if (!this.resizerShouldNotify || this.resizerShouldNotify(resizable)) {
-          resizable.notifyResize();
-        }
-      }, this);
-
-      this.fire('iron-resize', null, {
-        node: this,
-        bubbles: false
-      });
-    },
-
-    /**
-     * Used to assign the closest resizable ancestor to this resizable
-     * if the ancestor detects a request for notifications.
-     */
-    assignParentResizable: function(parentResizable) {
-      this._parentResizable = parentResizable;
-    },
-
-    /**
-     * Used to remove a resizable descendant from the list of descendants
-     * that should be notified of a resize change.
-     */
-    stopResizeNotificationsFor: function(target) {
-      var index = this._interestedResizables.indexOf(target);
-
-      if (index > -1) {
-        this._interestedResizables.splice(index, 1);
-      }
-    },
-
-    // TODO(cdata): Currently behaviors cannot define "abstract" methods.
-    // resizerShouldNotify: function(el) { return true; },
-
-    _parentResizableChanged: function(parentResizable) {
-      if (parentResizable) {
-        window.removeEventListener('resize', this._boundNotifyResize);
-      }
-    },
-
-    _onIronRequestResizeNotifications: function(event) {
-      var target = event.path ? event.path[0] : event.target;
-
-      if (target === this) {
-        return;
-      }
-
-      if (this._interestedResizables.indexOf(target) === -1) {
-        this._interestedResizables.push(target);
-      }
-
-      target.assignParentResizable(this);
-
-      event.stopPropagation();
-    }
-  };