Bug 1717642 - Add a pref to force full parse for OMT compiled JS scripts from the ScriptLoader. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D118494

dom/script/ScriptLoader.cpp

@@ -2622,6 +2622,10 @@ nsresult ScriptLoader::AttemptAsyncScriptCompile(ScriptLoadRequest* aRequest,
     nsresult rv = GetScriptSource(cx, aRequest, &maybeSource);
     NS_ENSURE_SUCCESS(rv, rv);
 
+    if (StaticPrefs::dom_script_loader_full_parse()) {
+      options.setForceFullParse();
+    }
+
     aRequest->mOffThreadToken =
         maybeSource.constructed<SourceText<char16_t>>()
             ? JS::CompileOffThread(

modules/libpref/init/StaticPrefList.yaml

@@ -2864,6 +2864,12 @@
   value: 0
   mirror: always
 
+# Force full parse on any external JS scripts that is being compiled off thread.
+- name: dom.script_loader.full_parse
+  type: bool
+  value: false
+  mirror: always
+
 # Is support for decoding external (non-inline) classic or module DOM scripts
 # (i.e. anything but workers) as UTF-8, then directly compiling without
 # inflating to UTF-16, enabled?