add back deepContains (got removed incorrectly in merge).

src/lib/dom-api.html

@@ -52,6 +52,28 @@
         Polymer.dom.flush();
       },
 
+      /**
+       * Check that the given node is a descendant of `this`,
+       * ignoring ShadowDOM boundaries
+       * @param {Node} node
+       * @return {Boolean} true if `node` is a descendant or equal to `this`
+       */
+      deepContains: function(node) {
+        // fast path, use shallow `contains`.
+        if (this.node.contains(node)) {
+          return true;
+        }
+        var n = node;
+        // wrap document for SD polyfill
+        var wrappedDocument = wrap(document);
+        // walk from node to `this` or `document`
+        while (n && n !== wrappedDocument && n !== this.node) {
+          // use logical parentnode, or native ShadowRoot host
+          n = Polymer.dom(n).parentNode || n.host;
+        }
+        return n === this.node;
+      },
+
       _lazyDistribute: function(host) {
         // note: only try to distribute if the root is not clean; this ensures
         // we don't distribute before initial distribution