Bypass ScriptValue in Document::createCSSStyleSheet.

ScriptPromise is perfectly happy with a v8::Local<v8::Value>, which is created
on the way to ScriptValue anyhow.

Change-Id: Ib9e6529bcac0262ffd2ddb89ce4de0cfe5587c81
Reviewed-on: https://chromium-review.googlesource.com/c/1316098Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605218}

third_party/blink/renderer/core/dom/document.cc

@@ -1139,8 +1139,7 @@ ScriptPromise Document::createCSSStyleSheet(ScriptState* script_state,
   CSSStyleSheet* sheet = CSSStyleSheet::Create(*this, options, exception_state);
   sheet->SetText(text, true /* allow_import_rules */, exception_state);
   sheet->SetAssociatedDocument(this);
-  return ScriptPromise::Cast(script_state,
-                             ScriptValue::From(script_state, sheet));
+  return ScriptPromise::Cast(script_state, ToV8(sheet, script_state));
 }
 
 CSSStyleSheet* Document::createCSSStyleSheetSync(