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

sky/engine/tonic/dart_converter.h

 // 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.
 
 #ifndef SKY_ENGINE_TONIC_DART_CONVERTER_H_
 #define SKY_ENGINE_TONIC_DART_CONVERTER_H_
 
 #include <string>
 #include "sky/engine/tonic/dart_state.h"
 #include "sky/engine/tonic/dart_string.h"
@@ skipping 59 matching lines @@
 struct DartConverterInteger {
   static Dart_Handle ToDart(T val) { return Dart_NewInteger(val); }
 
   static void SetReturnValue(Dart_NativeArguments args, T val) {
     Dart_SetIntegerReturnValue(args, val);
   }
 
   static T FromDart(Dart_Handle handle) {
     int64_t result = 0;
     Dart_IntegerToInt64(handle, &result);
-    return result;
+    return static_cast<T>(result);
   }
 
   static T FromArguments(Dart_NativeArguments args,
                          int index,
                          Dart_Handle& exception) {
     int64_t result = 0;
     Dart_GetNativeIntegerArgument(args, index, &result);
-    return result;
+    return static_cast<T>(result);
   }
 };
 
 template <>
 struct DartConverter<int> : public DartConverterInteger<int> {};
 
 template <>
 struct DartConverter<unsigned> : public DartConverterInteger<unsigned> {};
 
 template <>
@@ skipping 53 matching lines @@
   }
 };
 
 template <>
 struct DartConverter<float> : public DartConverterFloatingPoint<float> {};
 
 template <>
 struct DartConverter<double> : public DartConverterFloatingPoint<double> {};
 
 ////////////////////////////////////////////////////////////////////////////////
+// Enums
+
+template <typename T>
+struct DartConverterEnum {
+  static T FromArguments(Dart_NativeArguments args,
+                         int index,
+                         Dart_Handle& exception) {
+    Dart_Handle enum_handle = Dart_GetNativeArgument(args, index);
+    Dart_Handle index_handle =
+        Dart_GetField(enum_handle, DartState::Current()->index_handle());
+
+    uint64_t enum_index = 0;
+    Dart_IntegerToUint64(index_handle, &enum_index);
+    return static_cast<T>(enum_index);
+  }
+};
+
+////////////////////////////////////////////////////////////////////////////////
 // Strings
 
 template <>
 struct DartConverter<String> {
   static Dart_Handle ToDart(DartState* state, const String& val) {
     if (val.isEmpty())
       return Dart_EmptyString();
     return Dart_HandleFromWeakPersistent(state->string_cache().Get(val.impl()));
   }
 
@@ skipping 184 matching lines @@
 
 
 // Alias Dart_NewStringFromCString for less typing.
 inline Dart_Handle ToDart(const char* val) {
   return Dart_NewStringFromCString(val);
 }
 
 }  // namespace blink
 
 #endif  // SKY_ENGINE_TONIC_DART_CONVERTER_H_