Reduce boilerplate needed to configure mojo::Binding

mash/wm/accelerator_registrar_apptest.cc

Index: mash/wm/accelerator_registrar_apptest.cc
diff --git a/mash/wm/accelerator_registrar_apptest.cc b/mash/wm/accelerator_registrar_apptest.cc
index eaccd5b2e5dff94398e280f03c4629ebe4a961a0..0f5a7d9ccc8ba274b8de6e76710744def72d917b 100644
--- a/mash/wm/accelerator_registrar_apptest.cc
+++ b/mash/wm/accelerator_registrar_apptest.cc
@@ -29,9 +29,7 @@ class TestAcceleratorHandler : public AcceleratorHandler {
       : binding_(this),
         registrar_(std::move(registrar)),
         add_accelerator_result_(false) {
-    AcceleratorHandlerPtr handler;
-    binding_.Bind(GetProxy(&handler));
-    registrar_->SetHandler(std::move(handler));
+    registrar_->SetHandler(binding_.CreateInterfacePtrAndBind());
   }
   ~TestAcceleratorHandler() override {}