Add new chrome://proximity-auth WebUI for debugging Smart Lock.

components/proximity_auth.gypi

Index: components/proximity_auth.gypi
diff --git a/components/proximity_auth.gypi b/components/proximity_auth.gypi
index fe5f3be20c1c1d2e1ff419d152e0b1841996a2aa..be125164a5f93541fdf2bc0c33bb1c60b22fb309 100644
--- a/components/proximity_auth.gypi
+++ b/components/proximity_auth.gypi
@@ -106,5 +106,28 @@
         'cryptauth_proto',
       ],
     },
+    {
+      # GN version: //components/proximity_auth/webui
+      'target_name': 'proximity_auth_webui',
+      'type': 'static_library',
+      'dependencies': [
+        '../base/base.gyp:base',
+        '../content/content.gyp:content_browser',
+        'components_resources.gyp:components_resources',
+        'proximity_auth',
+        'cryptauth',
+      ],
+      'include_dirs': [
+        '..',
+      ],
+      'sources': [
+        'proximity_auth/webui/proximity_auth_ui.cc',
+        'proximity_auth/webui/proximity_auth_ui.h',
+        'proximity_auth/webui/proximity_auth_webui_constants.cc',
+        'proximity_auth/webui/proximity_auth_webui_constants.h',
+        'proximity_auth/webui/proximity_auth_webui_handler.cc',
+        'proximity_auth/webui/proximity_auth_webui_handler.h',
+      ],
+    },
   ],
 }