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

services/ui/ws/server_window_surface.cc

Index: services/ui/ws/server_window_surface.cc
diff --git a/services/ui/ws/server_window_surface.cc b/services/ui/ws/server_window_surface.cc
index 01de6021a8ed06c1b95be5dd8b4bc29e37ed9162..1a7c76eb5ad321486d377267d080d0aaee8378c0 100644
--- a/services/ui/ws/server_window_surface.cc
+++ b/services/ui/ws/server_window_surface.cc
@@ -50,8 +50,8 @@ void ServerWindowSurface::SubmitCompositorFrame(
       frame.delegated_frame_data->render_pass_list[0]->output_rect.size();
   // If the size of the CompostiorFrame has changed then destroy the existing
   // Surface and create a new one of the appropriate size.
-  if (local_frame_id_.is_null() || frame_size != last_submitted_frame_size_) {
-    if (!local_frame_id_.is_null())
+  if (!local_frame_id_.is_valid() || frame_size != last_submitted_frame_size_) {
+    if (local_frame_id_.is_valid())
       surface_factory_.Destroy(local_frame_id_);
     local_frame_id_ = surface_id_allocator_.GenerateId();
     surface_factory_.Create(local_frame_id_);
@@ -64,7 +64,7 @@ void ServerWindowSurface::SubmitCompositorFrame(
 }
 
 cc::SurfaceId ServerWindowSurface::GetSurfaceId() const {
-  if (local_frame_id_.is_null())
+  if (!local_frame_id_.is_valid())
     return cc::SurfaceId();
   return cc::SurfaceId(frame_sink_id_, local_frame_id_);
 }