[DevTools] Do not disable blocked URLs list when it's empty

third_party/WebKit/Source/devtools/front_end/network/BlockedURLsPane.js

 // Copyright (c) 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.
 /**
  * @implements {UI.ListWidget.Delegate}
  * @unrestricted
  */
 Network.BlockedURLsPane = class extends UI.VBox {
   constructor() {
     super(true);
@@ skipping 157 matching lines @@
 
   _removeAll() {
     this._manager.setBlockedPatterns([]);
   }
 
   /**
    * @return {!Promise<?>}
    */
   _update() {
     var enabled = this._manager.blockingEnabled();
-    this._list.element.classList.toggle('blocking-disabled', !enabled);
+    this._list.element.classList.toggle('blocking-disabled', !enabled && !!this._manager.blockedPatterns().length);
     this._enabledCheckbox.setChecked(enabled);
     this._list.clear();
     for (var pattern of this._manager.blockedPatterns())
       this._list.appendItem(pattern, true);
     return Promise.resolve();
   }
 
   /**
    * @param {string} url
    * @return {number}
@@ skipping 43 matching lines @@
     if (request.wasBlocked()) {
       var count = this._blockedCountForUrl.get(request.url()) || 0;
       this._blockedCountForUrl.set(request.url(), count + 1);
       this._updateThrottler.schedule(this._update.bind(this));
     }
   }
 };
 
 /** @type {?Network.BlockedURLsPane} */
 Network.BlockedURLsPane._instance = null;