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

ios/net/BUILD.gn

Index: ios/net/BUILD.gn
diff --git a/ios/net/BUILD.gn b/ios/net/BUILD.gn
index 65c9eac43a23e076ea20a89f0f6a4d0c78f9c965..fff941a9182c5f49b1f2583e5b5e33d13be56089 100644
--- a/ios/net/BUILD.gn
+++ b/ios/net/BUILD.gn
@@ -4,11 +4,11 @@
 
 import("//ios/build/config.gni")
 import("//testing/test.gni")
+import("//url/features.gni")
 
 source_set("net") {
   deps = [
     "//base",
-    "//base:i18n",
     "//net",
     "//url:url_features",
   ]
@@ -55,6 +55,10 @@ source_set("net") {
     "url_scheme_util.h",
     "url_scheme_util.mm",
   ]
+
+  if (!use_platform_icu_alternatives) {
+    deps += [ "//base:i18n" ]
+  }
 }
 
 test("ios_net_unittests") {