Revert of Move gn _run target generation into test().

tools/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.
 
 import("//testing/test.gni")
 
 defines = [ "GN_BUILD" ]
 
 static_library("gn_lib") {
   configs += [ "//build/config:precompiled_headers" ]
@@ skipping 223 matching lines @@
   ]
 
   deps = [
     ":gn_lib",
     ":last_commit_position",
     "//base",
     "//build/config/sanitizers:deps",
   ]
 }
 
+# TODO(GYP): Delete this after we've converted everything to GN.
+# The _run targets exist only for compatibility w/ GYP.
+group("gn_unittests_run") {
+  testonly = true
+  deps = [
+    ":gn_unittests",
+  ]
+}
+
 test("gn_unittests") {
   sources = [
     "action_target_generator_unittest.cc",
     "args_unittest.cc",
     "builder_unittest.cc",
     "c_include_iterator_unittest.cc",
     "command_format_unittest.cc",
     "config_unittest.cc",
     "config_values_extractors_unittest.cc",
     "escape_unittest.cc",
@@ skipping 51 matching lines @@
     "format_test_data/",
   ]
 
   deps = [
     ":gn_lib",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//testing/gtest",
   ]
 }