Create native_viewport_service, don't build it into mojo_shell unless Android

mojo/services/view_manager/ids.h

Index: mojo/services/view_manager/ids.h
diff --git a/mojo/services/view_manager/ids.h b/mojo/services/view_manager/ids.h
index 4a27c627b4e63db1a975e33ec213dfd6459520d6..0d1c48644790c27ec3604117a514486dc0a2adf9 100644
--- a/mojo/services/view_manager/ids.h
+++ b/mojo/services/view_manager/ids.h
@@ -7,7 +7,6 @@
 
 #include "mojo/services/public/cpp/view_manager/types.h"
 #include "mojo/services/public/cpp/view_manager/util.h"
-#include "mojo/services/view_manager/view_manager_export.h"
 
 namespace mojo {
 namespace service {
@@ -21,7 +20,7 @@ const ConnectionSpecificId kInvalidConnectionId = 0;
 const ConnectionSpecificId kWindowManagerConnection = 1;
 
 // Adds a bit of type safety to view ids.
-struct MOJO_VIEW_MANAGER_EXPORT ViewId {
+struct ViewId {
   ViewId(ConnectionSpecificId connection_id, ConnectionSpecificId view_id)
       : connection_id(connection_id),
         view_id(view_id) {}