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

ui/android/delegated_frame_host_android.cc

Index: ui/android/delegated_frame_host_android.cc
diff --git a/ui/android/delegated_frame_host_android.cc b/ui/android/delegated_frame_host_android.cc
index 2412a064cafee54b1f30112c9ce1ac3679e5ccf4..0acbf9cc7b4541ee680d0725e1d0a1fbe6a51200 100644
--- a/ui/android/delegated_frame_host_android.cc
+++ b/ui/android/delegated_frame_host_android.cc
@@ -225,7 +225,7 @@ void DelegatedFrameHostAndroid::UpdateContainerSizeinDIP(
 
 void DelegatedFrameHostAndroid::RegisterFrameSinkHierarchy(
     const cc::FrameSinkId& parent_id) {
-  if (!registered_parent_frame_sink_id_.is_null())
+  if (registered_parent_frame_sink_id_.is_valid())
     UnregisterFrameSinkHierarchy();
   registered_parent_frame_sink_id_ = parent_id;
   surface_manager_->RegisterSurfaceFactoryClient(frame_sink_id_, this);
@@ -233,7 +233,7 @@ void DelegatedFrameHostAndroid::RegisterFrameSinkHierarchy(
 }
 
 void DelegatedFrameHostAndroid::UnregisterFrameSinkHierarchy() {
-  if (registered_parent_frame_sink_id_.is_null())
+  if (!registered_parent_frame_sink_id_.is_valid())
     return;
   surface_manager_->UnregisterSurfaceFactoryClient(frame_sink_id_);
   surface_manager_->UnregisterFrameSinkHierarchy(