LibWeb: Add MediaList

This is a list of MediaQuery objects. Not to be confused with
`MediaQueryList`, which is concerned with firing events when a media
query's match-state changes.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -25,6 +25,7 @@ set(SOURCES
     CSS/ResolvedCSSStyleDeclaration.cpp
     CSS/DefaultStyleSheetSource.cpp
     CSS/Length.cpp
+    CSS/MediaList.cpp
     CSS/MediaQuery.cpp
     CSS/MediaQueryList.cpp
     CSS/Parser/Parser.cpp