Mojo: validate nullability in Java bindings.

mojo/public/tools/bindings/generators/java_templates/struct_definition.tmpl

 {% from "constant_definition.tmpl" import constant_def %}
 {% from "enum_definition.tmpl" import enum_def %}
 
 {% macro encode(variable, kind, offset, bit, level=0) %}
 {% if kind|is_pointer_array_kind %}
 {% set sub_kind = kind.kind %}
 if ({{variable}} == null) {
     encoder{{level}}.encodeNullPointer({{offset}});
 } else {
     org.chromium.mojo.bindings.Encoder encoder{{level + 1}} = encoder{{level}}.encodePointerArray({{variable}}.length, {{offset}});
     for (int i{{level}} = 0; i{{level}} < {{variable}}.length; ++i{{level}}) {
         {{encode(variable~'[i'~level~']', sub_kind, 'DataHeader.HEADER_SIZE + org.chromium.mojo.bindings.BindingsHelper.POINTER_SIZE * i'~level, 0, level+1)|indent(8)}}
     }
 }
 {% else %}
 encoder{{level}}.{{kind|encode_method(variable, offset, bit)}};
 {% endif %}
 {% endmacro %}
 
 {% macro decode(variable, kind, offset, bit, level=0) %}
 {% if kind|is_struct_kind or kind|is_pointer_array_kind %}
-org.chromium.mojo.bindings.Decoder decoder{{level+1}} = decoder{{level}}.readPointer({{offset}});
+org.chromium.mojo.bindings.Decoder decoder{{level+1}} = decoder{{level}}.readPointer({{offset}}, {{kind|is_nullable_kind|java_true_false}});
 {%   if kind|is_struct_kind %}
 {{variable}} = {{kind|java_type}}.decode(decoder{{level+1}});
 {%   else %}{# kind|is_pointer_array_kind #}
 if (decoder{{level+1}} == null) {
     {{variable}} = null;
 } else {
     DataHeader si{{level+1}} = decoder{{level+1}}.readDataHeader();
     {{variable}} = {{kind|new_array('si'~(level+1)~'.numFields')}};
     for (int i{{level+1}} = 0; i{{level+1}} < si{{level+1}}.numFields; ++i{{level+1}}) {
         {{decode(variable~'[i'~(level+1)~']', kind.kind, 'DataHeader.HEADER_SIZE + org.chromium.mojo.bindings.BindingsHelper.POINTER_SIZE * i'~(level+1), 0, level+1)|indent(8)}}
@@ skipping 68 matching lines @@
         org.chromium.mojo.bindings.Encoder encoder0 = encoder.getEncoderAtDataOffset(DEFAULT_STRUCT_INFO);
 {% endif %}
 {% for byte in struct.bytes %}
 {%   for packed_field in byte.packed_fields %}
         {{encode(packed_field.field|name, packed_field.field.kind, 8+packed_field.offset, packed_field.bit)|indent(8)}}
 {%   endfor %}
 {% endfor %}
     }
 }
 {% endmacro %}