MD History: promote menu button to show clear browsing data in narrow mode

chrome/browser/resources/md_history/history_toolbar.js

 // Copyright 2015 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({
   is: 'history-toolbar',
   properties: {
     // Number of history items currently selected.
     // TODO(calamity): bind this to
     // listContainer.selectedItem.selectedPaths.length.
@@ skipping 45 matching lines @@
       value: 0,
       reflectToAttribute: true,
       notify: true
     },
 
     // The start time of the query range.
     queryStartTime: String,
 
     // The end time of the query range.
     queryEndTime: String,
+
+    // Whether to show the menu promo (a tooltip that points at the menu button
+    // in narrow mode).
+    showMenuPromo_: {
+      type: Boolean,
+      value: function() {
+        return loadTimeData.getBoolean('showMenuPromo');
+      },
+    },
   },
 
   /**
    * Changes the toolbar background color depending on whether any history items
    * are currently selected.
    * @private
    */
   changeToolbarView_: function() {
     this.itemsSelected_ = this.count > 0;
   },
 
   /**
    * When changing the search term externally, update the search field to
    * reflect the new search term.
    * @param {string} search
    */
   setSearchTerm: function(search) {
     if (this.searchTerm == search)
       return;
 
     this.searchTerm = search;
     var searchField = /** @type {!CrToolbarElement} */(this.$['main-toolbar'])
                           .getSearchField();
     searchField.showAndFocus();
     searchField.setValue(search);
   },
 
+  /** @private */
+  onMenuPromoShown_: function() {
+    md_history.BrowserService.getInstance().menuPromoShown();
+  },
+
   /**
    * @param {!CustomEvent} event
    * @private
    */
   onSearchChanged_: function(event) {
     this.searchTerm = /** @type {string} */ (event.detail);
   },
 
   /** @private */
   onInfoButtonTap_: function() {
@@ skipping 40 matching lines @@
     // TODO(calamity): Fix the format of these dates.
     return loadTimeData.getStringF(
       'historyInterval', queryStartTime, queryEndTime);
   },
 
   /** @private */
   hasDrawerChanged_: function() {
     this.updateStyles();
   },
 });