Issue 5864 - Remove previous style sheet before adding one

include.preload.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 328 matching lines @@
   }
 };
 
 function ElemHide()
 {
   this.shadow = this.createShadowTree();
   this.style = null;
   this.tracer = null;
   this.inject = true;
   this.emulatedPatterns = null;
+  this.emulatedSelectors = null;
 
   this.elemHideEmulation = new ElemHideEmulation(
     this.addSelectors.bind(this),
     this.hideElements.bind(this)
   );
 }
 ElemHide.prototype = {
   selectorGroupSize: 200,
 
   createShadowTree()
@@ skipping 82 matching lines @@
     {
       // Insert the style rules inline if we have been instructed by the
       // background page to do so. This is usually the case, except on platforms
       // that do support user stylesheets via the chrome.tabs.insertCSS API
       // (Firefox 53 onwards for now and possibly Chrome in the near future).
       // Once all supported platforms have implemented this API, we can remove
       // the code below. See issue #5090.
       // Related Chrome and Firefox issues:
       // https://bugs.chromium.org/p/chromium/issues/detail?id=632009
       // https://bugzilla.mozilla.org/show_bug.cgi?id=1310026
       this.injectSelectors(selectors, filters);

[Manish Jethani, 2017/10/14 00:08:03]

We should also do the same for when styles are injected directly into the DOM.
For this we'll have to maintain two <style> elements, one for normal and one for
emulation, and injectSelectors would have to simply wipe the emulation style
sheet before adding any new selectors to it.

     }
     else
     {
       chrome.runtime.sendMessage({
         type: "elemhide.injectSelectors",
-        selectors
+        selectors,

[Manish Jethani, 2017/10/14 00:08:03]

Note that earlier in this function we're exiting if the list of selectors is
empty. This means if there are any style sheets already injected, they should be
removed, but they won't. We should make sure that if the list of selectors is
empty then there are no style sheets left in the fame. We need to update the
logic here a bit.

[Manish Jethani, 2017/10/14 13:38:18]

Done.

+        previousSelectors: this.emulatedSelectors
       });
+      this.emulatedSelectors = selectors;
     }
 
     if (this.tracer)
       this.tracer.addSelectors(selectors, filters);
   },
 
   hideElements(elements, filters)
   {
     for (let element of elements)
       hideElement(element);
@@ skipping 47 matching lines @@
     checkCollapse(event.target);
   }, true);
 
   document.addEventListener("load", event =>
   {
     let element = event.target;
     if (/^i?frame$/.test(element.localName))
       checkCollapse(element);
   }, true);
 }