Replaced is_null() with is_valid in SurfaceId and related classes.

ui/aura/mus/window_port_mus.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/aura/mus/window_port_mus.h"
 
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/transient_window_client.h"
 #include "ui/aura/mus/property_converter.h"
 #include "ui/aura/mus/surface_id_handler.h"
@@ skipping 203 matching lines @@
   GetPropertyConverter()->SetPropertyFromTransportValue(window_, property_name,
                                                         property_data);
 }
 
 void WindowPortMus::SetSurfaceIdFromServer(
     std::unique_ptr<SurfaceInfo> surface_info) {
   if (surface_info_) {
     const cc::SurfaceId& existing_surface_id = surface_info_->surface_id;
     cc::SurfaceId new_surface_id =
         surface_info ? surface_info->surface_id : cc::SurfaceId();
-    if (!existing_surface_id.is_null() &&
+    if (existing_surface_id.is_valid() &&
         existing_surface_id != new_surface_id) {
       // TODO(kylechar): Start return reference here?
     }
   }
   WindowPortMus* parent = Get(window_->parent());
   if (parent && parent->surface_id_handler_) {
     parent->surface_id_handler_->OnChildWindowSurfaceChanged(window_,
                                                              &surface_info);
   }
   surface_info_ = std::move(surface_info);
@@ skipping 123 matching lines @@
   change_data.property_name =
       GetPropertyConverter()->GetTransportNameForPropertyKey(key);
   // TODO(sky): investigate to see if we need to compare data. In particular do
   // we ever have a case where changing a property cascades into changing the
   // same property?
   if (!RemoveChangeByTypeAndData(ServerChangeType::PROPERTY, change_data))
     window_tree_client_->OnWindowMusPropertyChanged(this, key, std::move(data));
 }
 
 }  // namespace aura