Add unit tests target to GN build.

chrome/tools/convert_dict/BUILD.gn

+# Copyright 2015 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.
+
+source_set("lib") {
+  # Production code shouldn't be depending on this.
+  testonly = true
+
+  sources = [
+    "aff_reader.cc",
+    "aff_reader.h",
+    "dic_reader.cc",
+    "dic_reader.h",
+    "hunspell_reader.cc",
+    "hunspell_reader.h",
+  ]
+  configs += [ "//build/config/compiler:wexit_time_destructors" ]
+  deps = [
+    "//base",
+  ]
+}
+
+executable("convert_dict") {
+  # Production code shouldn't be depending on this.
+  testonly = true
+
+  sources = [
+    "convert_dict.cc",
+  ]
+  configs += [ "//build/config/compiler:wexit_time_destructors" ]
+  deps = [
+    ":lib",
+    "//base",
+    "//base:i18n",
+    "//third_party/hunspell",
+  ]
+}