IDL: Put generated union type containers in separate files

Source/modules/fetch/Request.h

Index: Source/modules/fetch/Request.h
diff --git a/Source/modules/fetch/Request.h b/Source/modules/fetch/Request.h
index 68615cce6a02b8e8d713295221f3ca8d0030b5fa..e3eb8b35ce2848fa11e7d04837a5f42e22179421 100644
--- a/Source/modules/fetch/Request.h
+++ b/Source/modules/fetch/Request.h
@@ -7,7 +7,6 @@
 
 #include "bindings/core/v8/Dictionary.h"
 #include "bindings/core/v8/ScriptWrappable.h"
-#include "bindings/modules/v8/UnionTypesModules.h"
 #include "modules/fetch/Body.h"
 #include "modules/fetch/FetchRequestData.h"
 #include "modules/fetch/Headers.h"
@@ -21,6 +20,7 @@ namespace blink {
 
 class BodyStreamBuffer;
 class RequestInit;
+class RequestOrUSVString;
 class WebServiceWorkerRequest;
 
 typedef RequestOrUSVString RequestInfo;