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

mojo/mojo_services.gypi

Index: mojo/mojo_services.gypi
diff --git a/mojo/mojo_services.gypi b/mojo/mojo_services.gypi
index 2ec0a1eb528735765c988ce857cb0815f60bc2db..ebd78ec3c1be617618778f65880ddd600dd8ca76 100644
--- a/mojo/mojo_services.gypi
+++ b/mojo/mojo_services.gypi
@@ -290,6 +290,22 @@
       ],
     },
     {
+      'target_name': 'mojo_native_viewport_service',
+      'type': 'loadable_module',
+      'dependencies': [
+        'mojo_native_viewport_bindings',
+        'mojo_native_viewport_service_lib',
+        '<(mojo_gles2_for_loadable_module)',
+        '<(mojo_system_for_loadable_module)',
+      ],
+      'export_dependent_settings': [
+        'mojo_native_viewport_bindings',
+      ],
+      'sources': [
+        'services/native_viewport/main.cc',
+      ],
+    },
+    {
       # GN version: //mojo/services/public/interfaces/navigation
       'target_name': 'mojo_navigation_bindings',
       'type': 'static_library',