Mojo C++ bindings: add StringTraits and ArrayTraits for STL types.

mojo/public/cpp/bindings/string_traits_stl.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_STRING_TRAITS_STL_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_STRING_TRAITS_STL_H_
+
+#include <string>
+
+#include "mojo/public/cpp/bindings/string_traits.h"
+
+namespace mojo {
+
+template <>
+struct StringTraits<std::string> {
+  static bool IsNull(const std::string& input) {
+    // std::string is always converted to non-null mojom string.
+    return false;
+  }
+
+  static void SetToNull(std::string* output) {
+    // std::string doesn't support null state. Set it to empty instead.
+    output->clear();
+  }
+
+  static size_t GetSize(const std::string& input) { return input.size(); }
+
+  static const char* GetData(const std::string& input) { return input.data(); }
+
+  static bool Read(StringDataView input, std::string* output) {
+    output->assign(input.storage(), input.size());
+    return true;
+  }
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_STRING_TRAITS_STL_H_