Soong support for namespaces

Bug: 65683273
Test: build/soong/scripts/diff_build_graphs.sh \
      --products=aosp_arm \
      'build/blueprint:work^ build/soong:work^' \
      'build/blueprint:work build/soong:work'
      # and see that the only changes were:
      # 1. adding some new files
      # 2. changing some line numbers
Test: m -j nothing # which runs unit tests

Change-Id: I6d3e52ef62c4cabe85b9a135a54de0e1a6aab29c
diff --git a/android/variable.go b/android/variable.go
index 13b5abf..dc24c1b 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -190,6 +190,8 @@
 
 	DeviceKernelHeaders []string `json:",omitempty"`
 	DistDir             *string  `json:",omitempty"`
+
+	NamespacesToExport []string `json:",omitempty"`
 }
 
 func boolPtr(v bool) *bool {