Gin: Consolidate all the Converter<Wrappable> subclasses.

gin/converter.h

 // Copyright 2013 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 GIN_CONVERTER_H_
 #define GIN_CONVERTER_H_
 
 #include <string>
 #include <vector>
 
 #include "base/strings/string_piece.h"
 #include "v8/include/v8.h"
 
 namespace gin {
 
-template<typename T>
+template<typename T, typename Enable = void>
 struct Converter {};
 
 template<>
 struct Converter<bool> {
   static v8::Handle<v8::Value> ToV8(v8::Isolate* isolate,
                                     bool val);
   static bool FromV8(v8::Isolate* isolate,
                      v8::Handle<v8::Value> val,
                      bool* out);
 };
@@ skipping 156 matching lines @@
 bool ConvertFromV8(v8::Isolate* isolate, v8::Handle<v8::Value> input,
                    T* result) {
   return Converter<T>::FromV8(isolate, input, result);
 }
 
 std::string V8ToString(v8::Handle<v8::Value> value);
 
 }  // namespace gin
 
 #endif  // GIN_CONVERTER_H_