[Cronet] Add BUILD.gn for legacy ios/CrNet project.

ios/net/protocol_handler_util.mm

Index: ios/net/protocol_handler_util.mm
diff --git a/ios/net/protocol_handler_util.mm b/ios/net/protocol_handler_util.mm
index 0609d3145f8b78f8d587284217576a76bd12f066..b9b215213ce293fa74e4643b13c2fbf4da380f9f 100644
--- a/ios/net/protocol_handler_util.mm
+++ b/ios/net/protocol_handler_util.mm
@@ -7,8 +7,6 @@
 #include <string>
 
 #include "base/base64.h"
-#include "base/i18n/encoding_detection.h"
-#include "base/i18n/icu_string_conversions.h"
 #include "base/logging.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/macros.h"
@@ -24,6 +22,11 @@
 #include "url/gurl.h"
 #include "url/url_features.h"
 
+#if !BUILDFLAG(USE_PLATFORM_ICU_ALTERNATIVES)
+#include "base/i18n/encoding_detection.h"  // nogncheck
+#include "base/i18n/icu_string_conversions.h"  // nogncheck
+#endif  // !BUILDFLAG(USE_PLATFORM_ICU_ALTERNATIVES)
+
 namespace {
 
 // "Content-Type" HTTP header.