Dart: Merge message pipe query and read into one native call.

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

Index: mojo/public/tools/bindings/generators/dart_templates/struct_definition.tmpl
diff --git a/mojo/public/tools/bindings/generators/dart_templates/struct_definition.tmpl b/mojo/public/tools/bindings/generators/dart_templates/struct_definition.tmpl
index 95ec615bf14463aae5b0db1132babaf97c00c43b..1818e4af71f117640c53e4f3622135cd42f787d5 100644
--- a/mojo/public/tools/bindings/generators/dart_templates/struct_definition.tmpl
+++ b/mojo/public/tools/bindings/generators/dart_templates/struct_definition.tmpl
@@ -31,7 +31,9 @@ class {{struct|name}} extends bindings.Struct {
   static {{struct|name}} deserialize(bindings.Message message) {
     var decoder = new bindings.Decoder(message);
     var result = decode(decoder);
-    decoder.excessHandles.forEach((h) => h.close());
+    if (decoder.excessHandles != null) {
+      decoder.excessHandles.forEach((h) => h.close());
+    }
     return result;
   }