[Chromecast] Define SYSTEM_NATIVE_UTF8 for Chromecast builds.

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index 0a0a6497b78edf8ec420649edeba1b6f721a917d..914f7cb912d2185604d61e02b50f833100ba560c 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -19,6 +19,7 @@
 
 import("//build/buildflag_header.gni")
 import("//build/config/allocator.gni")
+import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/config/sysroot.gni")
@@ -1027,7 +1028,7 @@ component("base") {
 
   # Allow more direct string conversions on platforms with native utf8
   # strings
-  if (is_mac || is_ios || is_chromeos) {
+  if (is_mac || is_ios || is_chromeos || is_chromecast) {
     defines += [ "SYSTEM_NATIVE_UTF8" ]
   }