Sky: Add a DartConverterEnum and use that for all our enum needs.

sky/engine/core/script/dom_dart_state.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/engine/config.h"
 #include "sky/engine/core/script/dom_dart_state.h"
 
 #include "sky/engine/core/dom/Document.h"
 #include "sky/engine/core/script/dart_loader.h"
 #include "sky/engine/tonic/dart_builtin.h"
 
 namespace blink {
 
 DOMDartState::DOMDartState(Document* document, const KURL& url)
     : document_(document), url_(url), loader_(adoptPtr(new DartLoader(this))) {
 }
 
 DOMDartState::~DOMDartState() {
 }
 
 void DOMDartState::DidSetIsolate() {
-  Scope dart_scope(this);
-  x_handle_.Set(this, Dart_NewStringFromCString("x"));
-  y_handle_.Set(this, Dart_NewStringFromCString("y"));
-  index_handle_.Set(this, Dart_NewStringFromCString("index"));
-  value_handle_.Set(this, Dart_NewStringFromCString("_value"));
+  x_handle_.Set(this, ToDart("x"));
+  y_handle_.Set(this, ToDart("y"));
+  value_handle_.Set(this, ToDart("_value"));
 
   Dart_Handle sky_library = DartBuiltin::LookupLibrary("dart:sky");
   color_class_.Set(this, Dart_GetType(sky_library, ToDart("Color"), 0, 0));
 }
 
 DOMDartState* DOMDartState::Current() {
   return static_cast<DOMDartState*>(DartState::Current());
 }
 
 Document* DOMDartState::CurrentDocument() {
   return Current()->document_.get();
 }
 
 LocalFrame* DOMDartState::CurrentFrame() {
   DCHECK(Current()->document_);
   return Current()->document_->frame();
 }
 
 LocalDOMWindow* DOMDartState::CurrentWindow() {
   DCHECK(Current()->document_);
   return Current()->document_->domWindow();
 }
 
 }  // namespace blink