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

mojo/public/cpp/bindings/string_traits_wtf.h

Index: mojo/public/cpp/bindings/string_traits_wtf.h
diff --git a/mojo/public/cpp/bindings/string_traits_wtf.h b/mojo/public/cpp/bindings/string_traits_wtf.h
index f65592cd5a90949f0bd8ddf0a7e3bd6f113fc972..4e330ae2e4a653b6c97f35bb3824b61ed220c242 100644
--- a/mojo/public/cpp/bindings/string_traits_wtf.h
+++ b/mojo/public/cpp/bindings/string_traits_wtf.h
@@ -22,9 +22,7 @@ struct StringTraits<WTF::String> {
 
   static const char* GetData(const WTF::String& input, void* context);
 
-  // TODO(yzshen): Use a public type, such as mojo::String::DataView, for
-  // |input|.
-  static bool Read(internal::String_Data* input, WTF::String* output);
+  static bool Read(StringDataView input, WTF::String* output);
 };
 
 }  // namespace mojo