[webnfc] Add default implementation for nfc mojo service.

device/nfc/nfc.gyp

Index: device/nfc/nfc.gyp
diff --git a/device/nfc/nfc.gyp b/device/nfc/nfc.gyp
index 9f17565e18ebb101eb6ccd050520b6026e490e38..2b12f37f9418b40a928824343e74fae77eaa0eab 100644
--- a/device/nfc/nfc.gyp
+++ b/device/nfc/nfc.gyp
@@ -60,5 +60,23 @@
         'nfc.mojom',
       ],
     },
+    {
+      # GN version: //device/nfc_mojo
+      'target_name': 'device_nfc_mojo',
+      'type': '<(component)',
+      'dependencies': [
+        '../../base/base.gyp:base',
+        '../../mojo/mojo_edk.gyp:mojo_system_impl',
+        '../../mojo/mojo_public.gyp:mojo_cpp_bindings',
+        'device_nfc_mojo_bindings',
+      ],
+      'defines': [
+        'DEVICE_NFC_IMPLEMENTATION',
+      ],
+      'sources': [
+        'nfc_impl_default.cc',
+        'nfc_impl.h',
+      ],
+    },
   ],
 }