Add a missing BUILD dep for app_child_process.mojom.

shell/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//mojo/public/mojo.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//testing/test.gni")
 
 # We don't support building in the component build since mojo apps are
@@ skipping 342 matching lines @@
       ":java",
       "//base:base_java",
     ]
   }
 }
 
 mojom("app_child_process_bindings") {
   sources = [
     "app_child_process.mojom",
   ]
+
+  deps = [
+    "//mojo/public/interfaces/application",
+  ]
 }
 
 mojom("external_application_registrar_bindings") {
   sources = [
     "external_application_registrar.mojom",
   ]
 
   deps = [
     "//mojo/public/interfaces/application",
   ]
@@ skipping 121 matching lines @@
 
     deps -= [
       ":lib",
       ":external_application_registrar_connection",
       ":external_application_registrar_bindings",
       "//shell/domain_socket",
       "//shell/domain_socket:tests",
     ]
   }
 }