Use user style sheets for emulation hiding filters if available

[mjethani]

Background

Currently ABP uses user style sheets only for standard hiding filters, but there have been recent changes that enable us to use them for emulation hiding filters as well:

1. Now we keep the style sheet for emulation hiding filters updated at all times so that there are no stale selectors (​revision 8399e34fff05)
2. If both tabs.insertCSS and tabs.removeCSS are available, we use user style sheets for some (but not all, i.e. only -abp-properties) emulation hiding filters (​revision 7247eb4632fa)

With a little bit of work, we can start using user style sheets for -abp-has and -abp-contains as well.

What to change

In include.preload.js, set the useInlineStyles property on the ElemHideEmulation instance to false if user style sheets are fully supported, otherwise set it to true.

Resolution

See #6504. We no longer use style sheets for any element hiding emulation filters (not even :-abp-properties()).

[mjethani]

Actually we don't have to traverse the entire DOM every time there's a mutation just for -abp-has and -abp-contains.

Let's take this document:

  <div id="n1">
    <div id="n1_1"></div>
    <div id="n1_2"></div>
    <div id="n1_4">Hello</div>
  </div>
  <div id="n2">
    <div id="n2_1"></div>
    <div id="n2_2"></div>
    <div id="n2_4">Hello</div>
  </div>
  <div id="n3">
    <div id="n3_1"></div>
    <div id="n3_2"></div>
    <div id="n3_4">Hello</div>
  </div>
  <div id="n4">
    <div id="n4_1"></div>
    <div id="n4_2"></div>
    <div id="n4_4">Hello</div>
  </div>

And let's say we have the selector :-abp-contains(Hello)

Now suppose a new node n2_3 is added to the DOM. In that case, we only need to do the following:

1. Run the filtering on n2_3, all its ancestors (n2 onwards), and its entire subtree
2. For each node that was previously affected by the filtering (n1_4, n2_4, n3_4, and n4_4), calculate the path and update it if it has changed

In this case, the path of n2_4 would have to be updated.

We don't need to go into n1, n3, and n4 because nothing has changed over there.

It's the same for when a node is deleted, except that any selectors that directly applied to the node or any of its descendants must be removed.

To recalculate and update the paths of the affected nodes, we'll have to maintain weak references to those nodes along with their previously calculated paths.

(Reposted from a previous email discussion.)

[mjethani]

Replying to mjethani:

Actually we don't have to traverse the entire DOM every time there's a mutation just for -abp-has and -abp-contains.

I'm covering this in #6437

​https://codereview.adblockplus.org/29714601/

[abpbot]

A commit referencing this issue has landed:
​Issue 6422 - Prefer CSS selectors for -abp-has and -abp-contains

[abpbot]

A commit referencing this issue has landed:
​Issue 6422 - Prefer CSS selectors for -abp-has and -abp-contains