Add chrome perf tests and sniffer to GN build.

chrome/tools/BUILD.gn

Index: chrome/tools/BUILD.gn
diff --git a/chrome/tools/BUILD.gn b/chrome/tools/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..0adca4b06bdcfa133da30339871953b2d893d99f
--- /dev/null
+++ b/chrome/tools/BUILD.gn
@@ -0,0 +1,13 @@
+# 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.
+
+# This target just provides references to the Chrome tools to bring them into
+# the build.
+group("tools") {
+  testonly = true
+  deps = [
+    # TODO(GYP) re-enable this. Currently it's giving linker errors about Mojo.
+    #"//chrome/tools/service_discovery_sniffer",
+  ]
+}