Add proto definitions for messages used by CryptAuth APIs and the authentication protocol.

components/proximity_auth/cryptauth/proto/BUILD.gn

Index: components/proximity_auth/cryptauth/proto/BUILD.gn
diff --git a/components/enhanced_bookmarks/proto/BUILD.gn b/components/proximity_auth/cryptauth/proto/BUILD.gn
similarity index 59%
copy from components/enhanced_bookmarks/proto/BUILD.gn
copy to components/proximity_auth/cryptauth/proto/BUILD.gn
index 579884aba01e55ad2821a7ed926ccadc11a026ff..5beee2a5a375f8ca539143cf8e8846bd7db97f50 100644
--- a/components/enhanced_bookmarks/proto/BUILD.gn
+++ b/components/proximity_auth/cryptauth/proto/BUILD.gn
@@ -2,12 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//third_party/protobuf/proto_library.gni")
+import ("//third_party/protobuf/proto_library.gni")
 
+# GYP version: //components/proximity_auth.gypi:cryptauth_proto
 proto_library("proto") {
   sources = [
-    "cluster.proto",
-    "metadata.proto",
-    "search.proto",
+    "cryptauth_api.proto",
   ]
 }