Add GN targets for mojom generator

mojo/BUILD.gn

Index: mojo/BUILD.gn
diff --git a/components/language_usage_metrics/BUILD.gn b/mojo/BUILD.gn
similarity index 55%
copy from components/language_usage_metrics/BUILD.gn
copy to mojo/BUILD.gn
index 88ad430bd5d7fa51b30734c134e38914e8ab72cd..61713162e75434e1937a42314cbc04121408de7c 100644
--- a/components/language_usage_metrics/BUILD.gn
+++ b/mojo/BUILD.gn
@@ -2,13 +2,10 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("language_usage_metrics") {
-  sources = [
-    "language_usage_metrics.cc",
-    "language_usage_metrics.h",
-  ]
-
+group("mojo") {
   deps = [
-    "//base",
+    "//mojo/public/cpp/bindings",
+    "//mojo/public/interfaces/bindings/tests:test_interfaces",
+    "//mojo/public/js/bindings",
   ]
 }