Roll Polymer elements

third_party/polymer/v1_0/components-chromium/app-layout/app-scroll-effects/effects/waterfall-extracted.js

+/**
+   * Toggles the shadow property in app-header when content is scrolled to create a sense of depth
+   * between the element and the content underneath.
+   */
+  Polymer.AppLayout.registerEffect('waterfall', {
+    /**
+     *  @this Polymer.AppLayout.ElementWithBackground
+     */
+    run: function run(p, y) {
+      this.shadow = this.isOnScreen() && this.isContentBelow();
+    }
+  });