Add data dependency directories for blink_tests in BUILD.gn.

BUILD.gn

 # Copyright (c) 2013 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 is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 899 matching lines @@
     if (is_mac) {
       deps += [
         "//breakpad:dump_syms($host_toolchain)",
         "//components/test_runner:layout_test_helper",
       ]
     }
 
     if (is_linux) {
       deps += [ "//breakpad:dump_syms($host_toolchain)" ]
     }
+
+    data = [
+      "//third_party/WebKit/LayoutTests/",
+      "//third_party/WebKit/Tools/Scripts/",
+    ]
   }
 }
 
 # Add a dummy target for compatibility w/ GYP
 group("chromium_swarm_tests") {
 }
 
 group("chromium_builder_perf") {
   testonly = true
 
@@ skipping 115 matching lines @@
   assert(target_name != "")  # Mark as used.
   sources = invoker.actual_sources
   assert(
       sources == invoker.actual_sources,
       "Do not use a platform name in your output directory (found \"$root_build_dir\"). http://crbug.com/548283")
 }
 
 assert_valid_out_dir("_unused") {
   actual_sources = [ "$root_build_dir/foo" ]
 }