[MD Bookmarks] Add routing.

chrome/browser/resources/md_bookmarks/router.js

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+Polymer({
+  /**
+   * This element is a one way bound interface that routes the page URL to
+   * the searchTerm and selectedId. Clients must initialize themselves by
+   * reading the router's fields after attach.
+   */
+  is: 'bookmarks-router',
+
+  properties: {
+    // Parameter q is routed to the searchTerm.
+    // Parameter id is routed to the selectedId.
+    queryParams_: Object,
+
+    searchTerm: {
+      type: String,
+      observer: 'onSearchTermChanged_',
+    },
+
+    /** @type {?string} */
+    selectedId: {
+      type: String,
+      observer: 'onSelectedChanged_',
+    },
+  },
+
+  observers: [
+    'onQueryChanged_(queryParams_.*)',
+  ],
+
+  /** @private */
+  onQueryChanged_: function() {
+    this.searchTerm = this.queryParams_.q || '';
+    this.selectedId = this.queryParams_.id;
+
+    if (this.searchTerm) {
+      this.fire('search-term-changed', this.searchTerm);
+    } else {
+      this.fire('selected-folder-changed', this.selectedId);
+    }
+  },
+
+  /** @private */
+  onSelectedChanged_: function() {
+    this.set('queryParams_.id', this.selectedId || null);
+  },
+
+  /** @private */
+  onSearchTermChanged_: function() {
+    this.set('queryParams_.q', this.searchTerm || null);
+  },
+});