LibWeb: Implement MediaQuery matching :^)

Currently, `evaluate()` recalculates whether the MediaQuery matches or
not, and stores it in `m_matches`, which users can query using
`matches()`. This allows us to know when the match-state changes, which
is required to fire MediaQueryList's change event.

Userland/Libraries/LibWeb/CSS/MediaList.cpp

@@ -67,4 +67,21 @@ void MediaList::delete_medium(String medium)
     // FIXME: If nothing was removed, then throw a NotFoundError exception.
 }
 
+bool MediaList::evaluate(DOM::Window const& window)
+{
+    for (auto& media : m_media)
+        media.evaluate(window);
+
+    return matches();
+}
+
+bool MediaList::matches() const
+{
+    for (auto& media : m_media) {
+        if (media.matches())
+            return true;
+    }
+    return false;
+}
+
 }