Dart: Simplifies the handle watcher. Various cleanups and bugfixes.

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

 {#--- Begin #}
 
 class {{struct.name}} {
 {#--- Enums #}
 {%- from "enum_definition.tmpl" import enum_def %}
 {%  for enum in struct.enums %}
   {{enum_def("  static ", enum)}}
 {%-  endfor %}
 
 
@@ skipping 39 matching lines @@
   }
 
   static void encode(bindings.MojoEncoder encoder, {{struct.name}} val) {
     var packed;
     encoder.writeUint32({{struct.name}}.encodedSize);
     encoder.writeUint32({{struct.packed.packed_fields|length}});
 {%- for byte in struct.bytes %}
 {%-   if byte.packed_fields|length > 1 %}
     packed = 0;
 {%-     for packed_field in byte.packed_fields %}
-    packed |= (val.{{packed_field.field.name}} & 1) << {{packed_field.bit}};
+    packed |= ((val.{{packed_field.field.name}} ? 1 : 0) & 1) << {{packed_field.bit}};
 {%-     endfor %}
     encoder.writeUint8(packed);
 {%-   else %}
 {%-     for packed_field in byte.packed_fields %}
     encoder.{{packed_field.field.kind|encode_snippet}}val.{{packed_field.field.name}});
 {%-     endfor %}
 {%-   endif %}
 {%-   if byte.is_padding %}
     encoder.skip(1);
 {%-   endif %}
 {%- endfor %}
   }
 }