Mojo C++ bindings: switch the existing usage of StructTraits to use the new data view interface.

mojo/public/tools/bindings/generators/cpp_templates/struct_data_view_declaration.tmpl

Index: mojo/public/tools/bindings/generators/cpp_templates/struct_data_view_declaration.tmpl
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/struct_data_view_declaration.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/struct_data_view_declaration.tmpl
index be7043a4f51a9b842fb8c9ac4f44b98bdc9c7e5f..41c96d36f96421ed3c30bc16e92e2d5fbcf03e0b 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/struct_data_view_declaration.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/struct_data_view_declaration.tmpl
@@ -4,18 +4,12 @@ class {{struct.name}}DataView {
       internal::{{struct.name}}_Data* data,
       mojo::internal::SerializationContext* context);
 
-  // Whether the data represents a null struct.
-  // Note: Must not access the following methods if is_null() returns true.
-  bool is_null() const { return !data_; }
-
 {%- for pf in struct.packed.packed_fields_in_ordinal_order %}
 {%-   set kind = pf.field.kind -%}
 {%-   set name = pf.field.name -%}
 {%-   if kind|is_struct_kind or kind|is_array_kind or kind|is_string_kind %}
   template <typename UserType>
   bool Read{{name|under_to_camel}}(UserType* value) {
-    DCHECK(!is_null());
-
 {%-  if pf.min_version != 0 %}
     auto pointer = data_->header_.version >= {{pf.min_version}}
                    ? data_->{{name}}.ptr : nullptr;