Move GN build files for cacheinvalidation into the main tree.

build/secondary/third_party/cacheinvalidation/src/google/cacheinvalidation/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("//third_party/protobuf/proto_library.gni")
-
-proto_library("cacheinvalidation_proto_cpp") {
-  # Depend on cacheinvalidation instead.
-  visibility = [ "//third_party/cacheinvalidation/*" ]
-
-  sources = [
-    "client.proto",
-    "client_gateway.proto",
-    "client_protocol.proto",
-    "client_test_internal.proto",
-    "types.proto",
-  ]
-
-  if (!is_android) {
-    sources += [
-      "android_channel.proto",
-      "channel_common.proto",
-    ]
-  }
-
-  proto_out_dir = "google/cacheinvalidation"
-}