Convert //mash to define service names in mojom

mash/catalog_viewer/public/interfaces/BUILD.gn

Index: mash/catalog_viewer/public/interfaces/BUILD.gn
diff --git a/mash/session/public/interfaces/BUILD.gn b/mash/catalog_viewer/public/interfaces/BUILD.gn
similarity index 69%
copy from mash/session/public/interfaces/BUILD.gn
copy to mash/catalog_viewer/public/interfaces/BUILD.gn
index c4c687528573f0d0be8ca5918b18205347f60767..b1ea7722c51476c635c9d83d7a982c2d2db49e30 100644
--- a/mash/session/public/interfaces/BUILD.gn
+++ b/mash/catalog_viewer/public/interfaces/BUILD.gn
@@ -4,8 +4,14 @@
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
-mojom("interfaces") {
+group("interfaces") {
+  deps = [
+    ":constants",
+  ]
+}
+
+mojom("constants") {
   sources = [
-    "session.mojom",
+    "constants.mojom",
   ]
 }