Mojo C++ bindings: provide data view for all object types.

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"
+#include "mojo/public/cpp/bindings/string_data_view.h"
 
 namespace mojo {
 
-// Access to the contents of a serialized string.
-class StringDataView {
- public:
-  explicit StringDataView(internal::String_Data* data) : data_(data) {
-    DCHECK(data_);
-  }
-
-  const char* storage() const { return data_->storage(); }
-
-  size_t size() const { return data_->size(); }
-
- private:
-  internal::String_Data* data_;
-};
-
 // This must be specialized for any type |T| to be serialized/deserialized as
 // a mojom string.
 //
 // Imagine you want to specialize it for CustomString, usually you need to
 // implement:
 //
 //   template <T>
 //   struct StringTraits<CustomString> {
 //     // These two methods are optional. Please see comments in struct_traits.h
 //     static bool IsNull(const CustomString& input);
 //     static void SetToNull(CustomString* output);
 //
 //     static size_t GetSize(const CustomString& input);
 //     static const char* GetData(const CustomString& input);
 //
+//     // The caller guarantees that |!input.is_null()|.
 //     static bool Read(StringDataView input, CustomString* output);
 //   };
 //
 // In some cases, you may need to do conversion before you can return the size
 // and data as 8-bit characters for serialization. (For example, CustomString is
 // UTF-16 string). In that case, you can add two optional methods:
 //
 //   static void* SetUpContext(const CustomString& input);
 //   static void TearDownContext(const CustomString& input, void* context);
 //
 // And then you append a second parameter, void* context, to GetSize() and
 // GetData():
 //
 //   static size_t GetSize(const CustomString& input, void* context);
 //   static const char* GetData(const CustomString& input, void* context);
 //
 // If a CustomString instance is not null, the serialization code will call
 // SetUpContext() at the beginning, and pass the resulting context pointer to
 // GetSize()/GetData(). After serialization is done, it calls TearDownContext()
 // so that you can do any necessary cleanup.
 //
 template <typename T>
 struct StringTraits;
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_STRING_TRAITS_H_