Issue 5864 - Remove previous style sheet before adding one

include.preload.js

Index: include.preload.js
===================================================================
--- a/include.preload.js
+++ b/include.preload.js
@@ -341,16 +341,17 @@
 
 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,
@@ -449,18 +450,20 @@
       // 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)
   {