MD settings: Storage: Add DELETE button for deleting Drive offline files.

chrome/browser/resources/settings/device_page/storage.js

 // Copyright 2016 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.
 
 /**
  * @fileoverview
  * 'settings-storage' is the settings subpage for storage settings.
  */
 cr.exportPath('settings');
 
@@ skipping 37 matching lines @@
       type: Boolean,
       value: false,
     },
 
     /** @private */
     isGuest_: {
       type: Boolean,
       value: function() { return loadTimeData.getBoolean('isGuest'); }
     },
 
+    /** @private */
+    hasDriveCache_: {
+      type: Boolean,
+      value: false
+    },
+
     /** @private {settings.StorageSizeStat} */
     sizeStat_: Object,
   },
 
   /**
    * Timer ID for periodic update.
    * @private {number}
    */
   updateTimerId_: -1,
 
@@ skipping 51 matching lines @@
     chrome.send('openDownloads');
   },
 
   /**
    * Handler for tapping the "Offline files" item.
    * @param {!Event} e
    * @private
    */
   onDriveCacheTap_: function(e) {
     e.preventDefault();
-    this.$.storageDriveCache.open();
+    if (this.hasDriveCache_)
+      this.$.storageDriveCache.open();
   },
 
   /**
    * Handler for tapping the "Browsing data" item.
    * @private
    */
   onBrowsingDataTap_: function() {
     settings.navigateTo(settings.Route.CLEAR_BROWSER_DATA);
   },
 
@@ skipping 28 matching lines @@
    * @param {string} size Formatted string representing the size of Downloads.
    * @private
    */
   handleDownloadsSizeChanged_: function(size) {
     this.$.downloadsSize.textContent = size;
   },
 
   /**
    * @param {string} size Formatted string representing the size of Offline
    *     files.
+   * @param {boolean} hasCache True if the device has at least one offline file.
    * @private
    */
-  handleDriveCacheSizeChanged_: function(size) {
+  handleDriveCacheSizeChanged_: function(size, hasCache) {
     this.$.driveCacheSize.textContent = size;
+    this.hasDriveCache_ = hasCache;
   },
 
   /**
    * @param {string} size Formatted string representing the size of Browsing
    *     data.
    * @private
    */
   handleBrowsingDataSizeChanged_: function(size) {
     this.$.browsingDataSize.textContent = size;
   },
@@ skipping 89 matching lines @@
     switch (spaceState) {
       case settings.StorageSpaceState.LOW:
         return 'space-low';
       case settings.StorageSpaceState.CRITICALLY_LOW:
         return 'space-critically-low';
       default:
         return '';
     }
   },
 });