Change TypeConverter<X,Y>::ConvertFrom and ConvertTo into a single symmetric

mojo/common/common_type_converters.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 MOJO_COMMON_COMMON_TYPE_CONVERTERS_H_
 #define MOJO_COMMON_COMMON_TYPE_CONVERTERS_H_
 
 #include "base/strings/string16.h"
 #include "base/strings/string_piece.h"
 #include "mojo/common/mojo_common_export.h"
 #include "mojo/public/cpp/bindings/string.h"
 #include "mojo/public/cpp/bindings/type_converter.h"
 
 class GURL;
 
 namespace mojo {
 
 template <>
-class MOJO_COMMON_EXPORT TypeConverter<String, base::StringPiece> {
- public:
-  static String ConvertFrom(const base::StringPiece& input);
-  static base::StringPiece ConvertTo(const String& input);
+struct MOJO_COMMON_EXPORT TypeConverter<String, base::StringPiece> {
+  static String Convert(const base::StringPiece& input);
 };
 
 template <>
-class MOJO_COMMON_EXPORT TypeConverter<String, base::string16> {
- public:
-  static String ConvertFrom(const base::string16& input);
-  static base::string16 ConvertTo(const String& input);
+struct MOJO_COMMON_EXPORT TypeConverter<base::StringPiece, String> {
+  static base::StringPiece Convert(const String& input);
 };
 
 template <>
-class MOJO_COMMON_EXPORT TypeConverter<String, GURL> {
- public:
-  static String ConvertFrom(const GURL& input);
-  static GURL ConvertTo(const String& input);
+struct MOJO_COMMON_EXPORT TypeConverter<String, base::string16> {
+  static String Convert(const base::string16& input);
+};
+
+template <>
+struct MOJO_COMMON_EXPORT TypeConverter<base::string16, String> {
+  static base::string16 Convert(const String& input);
+};
+
+template <>
+struct MOJO_COMMON_EXPORT TypeConverter<String, GURL> {
+  static String Convert(const GURL& input);
+};
+
+template <>
+struct MOJO_COMMON_EXPORT TypeConverter<GURL, String> {
+  static GURL Convert(const String& input);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_COMMON_COMMON_TYPE_CONVERTERS_H_