feat: Removed legacy stylesheets config and implement c++ mods backen… (#9131)

src/dom/base/Document-cpp.patch

@@ -0,0 +1,20 @@
+diff --git a/dom/base/Document.cpp b/dom/base/Document.cpp
+index a16bef739fcde0f14ba7e53e0acfa3aa2ee1dd3a..78b9d112a56b3d909e31eb4351ee9f3b06c4ef92 100644
+--- a/dom/base/Document.cpp
++++ b/dom/base/Document.cpp
+@@ -3332,6 +3332,15 @@ void Document::FillStyleSetUserAndUASheets() {
+ 
+   ServoStyleSet& styleSet = EnsureStyleSet();
+   for (StyleSheet* sheet : *sheetService->UserStyleSheets()) {
++    // If the url starts with "chrome://" and ends with 'zen-themes.css', then
++    // skip it if the document is in a chrome docshell.
++    // This is to avoid loading the user chrome stylesheet in the content
++    // process, which is not allowed.
++    auto spec = sheet->GetSheetURI()->GetSpecOrDefault();
++    if (!IsInChromeDocShell() && StringBeginsWith(spec, "file://"_ns) &&
++        StringEndsWith(spec, "zen-themes.css"_ns)) {
++      continue;
++    }
+     styleSet.AppendStyleSheet(*sheet);
+   }
+