Bug 285160 – Improve DOMStringList::contains() from O(n) to O(1)

• Component: DOM
• Status: RESOLVED FIXED

[Karl Dubost]

https://searchfox.org/wubkat/rev/36d40c7dfd972e688c9c0febea6821825a85d6ac/Source/WebCore/dom/DOMStringList.cpp#38-48
```cpp
bool DOMStringList::contains(const String& string) const
{
    // FIXME: Currently, all consumers of DOMStringList store fairly small lists and thus an O(n)
    //        algorithm is OK.  But this may need to be optimized if larger amounts of data are
    //        stored in m_strings.
    for (auto& value : m_strings) {
        if (value == string)
            return true;
    }
    return false;
}
```

[Karl Dubost]

It should be possible to initialize an unordered_string with all the strings and making it private.

   if (!m_stringSet) { m_stringSet.emplace(m_strings.begin(), m_strings.end()); }

Then the contains function could return a result with 

    m_stringSet->find(string) != m_stringSet->end();

[Radar WebKit Bug Importer]

<rdar://problem/142250869>

[Alexsander Borges Damaceno]

Pull request: https://github.com/WebKit/WebKit/pull/38526

[EWS]

Committed 289769@main (c430a96674ce): <https://commits.webkit.org/289769@main>

Reviewed commits have been landed. Closing PR #38526 and removing active labels.