Convert i18n_process.css to use /deep/ instead of ::shadow and add tests.

chrome/test/data/BUILD.gn

Index: chrome/test/data/BUILD.gn
diff --git a/chrome/test/data/BUILD.gn b/chrome/test/data/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..ef59dc6b11dca9e302f3b508f73cf4a5709c6412
--- /dev/null
+++ b/chrome/test/data/BUILD.gn
@@ -0,0 +1,14 @@
+# 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.
+
+import("//tools/grit/grit_rule.gni")
+
+grit("webui_test_resources") {
+  source = "webui_test_resources.grd"
+  outputs = [
+    "chrome/test/data/grit/webui_test_resources.h",
+    "webui_test_resources.pak",
+  ]
+  output_dir = "$root_gen_dir/chrome"
+}