Add chrome perf tests and sniffer to GN build.

chrome/tools/service_discovery_sniffer/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/features.gni")
+
+executable("service_discovery_sniffer") {
+  testonly = true
+  sources = [
+    "service_discovery_sniffer.cc",
+    "service_discovery_sniffer.h",
+  ]
+
+  deps = [
+    "//base",
+    "//base/test:test_support",
+    "//chrome/utility",
+    "//net",
+  ]
+
+  if (enable_webrtc) {
+    deps += [ "//third_party/libjingle:libjingle_webrtc" ]
+  }
+}