Mojo C++ bindings: support mapping mojo string to WTF::String.

mojo/public/cpp/bindings/lib/array_serialization_traits.h

 // Copyright 2016 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_PUBLIC_CPP_BINDINGS_LIB_ARRAY_SERIALIZATION_TRAITS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_ARRAY_SERIALIZATION_TRAITS_H_
 
 #include <stddef.h>
 #include <string.h>  // For |memcpy()|.
 
 #include <limits>
 #include <type_traits>
 #include <utility>
 #include <vector>
 
 #include "base/logging.h"
 #include "mojo/public/cpp/bindings/lib/array_internal.h"
 #include "mojo/public/cpp/bindings/lib/serialization_forward.h"
 #include "mojo/public/cpp/bindings/lib/template_util.h"
 #include "mojo/public/cpp/bindings/lib/validation_errors.h"
 
+namespace WTF {
+class String;
+}
+
 namespace mojo {
 namespace internal {
 
 template <typename ArrayType,
           typename ElementType,
           typename ElementDataType,
           bool is_union = IsUnionDataType<
               typename RemovePointer<ElementDataType>::type>::value>
 struct ArraySerializer;
 
@@ skipping 143 matching lines @@
       if (!Deserialize_(input->at(i), &result[i], context))
         success = false;
     }
     output->Swap(&result);
     return success;
   }
 
  private:
   template <typename T,
             bool is_array = IsSpecializationOf<Array, T>::value,
-            bool is_string = std::is_same<T, String>::value>
+            bool is_string = std::is_same<T, String>::value ||
+                             std::is_same<T, WTF::String>::value>
   struct SerializeCaller {
     static void Run(T input,
                     Buffer* buf,
                     typename WrapperTraits<T>::DataType* output,
                     const ArrayValidateParams* validate_params) {
       DCHECK(!validate_params)
           << "Struct type should not have array validate params";
 
       Serialize_(std::move(input), buf, output);
     }
@@ skipping 223 matching lines @@
     *output = nullptr;
     return true;
   }
 };
 
 }  // namespace internal
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_ARRAY_SERIALIZATION_TRAITS_H_