Fix SysStrings unit test failure on Chromecast

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index 25fc7c063e2280a9ef57d021feda7fdd2ffee030..b2d1280a972c009cc51f506a0531c1c7ba352c0a 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -1419,6 +1419,8 @@ test("base_unittests") {
     "win/wrapped_window_proc_unittest.cc",
   ]
 
+  defines = []
+
   deps = [
     ":base",
     ":i18n",
@@ -1435,6 +1437,12 @@ test("base_unittests") {
     "//third_party/icu",
   ]
 
+  # Allow more direct string conversions on platforms with native utf8
+  # strings
+  if (is_mac || is_ios || is_chromeos) {
+    defines += [ "SYSTEM_NATIVE_UTF8" ]
+  }
+
   if (is_android) {
     apk_deps = [
       ":base_java",
@@ -1469,7 +1477,7 @@ test("base_unittests") {
   if (is_linux) {
     sources -= [ "file_version_info_unittest.cc" ]
     sources += [ "nix/xdg_util_unittest.cc" ]
-    defines = [ "USE_SYMBOLIZE" ]
+    defines += [ "USE_SYMBOLIZE" ]
     if (use_glib) {
       configs += [ "//build/config/linux:glib" ]
     }