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

sky/engine/core/painting/TransferMode.cpp

-// 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/painting/TransferMode.h"
-
-#include "sky/engine/core/script/dom_dart_state.h"
-#include "sky/engine/tonic/dart_builtin.h"
-#include "sky/engine/tonic/dart_error.h"
-#include "sky/engine/tonic/dart_value.h"
-
-namespace blink {
-
-// If this fails, it's because SkXfermode has changed. We need to change
-// TransferMode.dart to ensure the TransferMode enum is in sync with the C++
-// values.
-COMPILE_ASSERT(SkXfermode::kLastMode == 28, Need_to_update_TransferMode_dart);
-
-// Convert dart_mode => SkXfermode::Mode.
-SkXfermode::Mode DartConverter<TransferMode>::FromArgumentsWithNullCheck(
-    Dart_NativeArguments args,
-    int index,
-    Dart_Handle& exception) {
-  SkXfermode::Mode result;
-
-  Dart_Handle dart_mode = Dart_GetNativeArgument(args, index);
-  DCHECK(!LogIfError(dart_mode));
-
-  Dart_Handle value =
-      Dart_GetField(dart_mode, DOMDartState::Current()->index_handle());
-
-  uint64_t mode = 0;
-  Dart_Handle rv = Dart_IntegerToUint64(value, &mode);
-  DCHECK(!LogIfError(rv));
-
-  result = static_cast<SkXfermode::Mode>(mode);
-  return result;
-}
-
-} // namespace blink