Mojo C++ bindings: expose public <struct>DataView and StringDataView.

mojo/public/cpp/bindings/string_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_STRING_TRAITS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_STRING_TRAITS_H_
 
+#include "base/logging.h"
+#include "mojo/public/cpp/bindings/lib/array_internal.h"
+
 namespace mojo {
 
+// Access to a string inside a mojo message.
+class StringDataView {
+ public:
+  explicit StringDataView(internal::String_Data* data) : data_(data) {}
+
+  // Whether the data represents a null string.
+  // Note: Must not access the following methods if this method returns true.
+  bool is_null() const { return !data_; }
+
+  const char* storage() const {
+    DCHECK(!is_null());
+    return data_->storage();
+  }
+
+  size_t size() const {
+    DCHECK(!is_null());
+    return data_->size();
+  }
+
+ private:
+  internal::String_Data* data_;
+};
+
 // This must be specialized for any UserType to be serialized/deserialized as
 // a mojom string.
 //
 // TODO(yzshen): This is work in progress. Add better documentation once the
 // interface becomes more stable.
 template <typename UserType>
 struct StringTraits;
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_STRING_TRAITS_H_