Set U_CHARSET_IS_UTF8 to 1 in BUILD.gn

BUILD.gn

 # Copyright 2014 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("//third_party/icu/config.gni")
 
 # Meta target that includes both icuuc and icui18n. Most targets want both.
 # You can depend on the individually if you need to.
 group("icu") {
   deps = [
     ":icui18n",
     ":icuuc",
   ]
 }
 
 # Shared config used by ICU and all dependents.
 config("icu_config") {
   defines = [
     "U_USING_ICU_NAMESPACE=0",
     "U_ENABLE_DYLOAD=0",
+    "U_CHARSET_IS_UTF8=1",
   ]
 
   if (component_mode != "shared_library") {
     defines += [ "U_STATIC_IMPLEMENTATION" ]
   }
 
   include_dirs = [
     "source/common",
     "source/i18n",
   ]
@@ skipping 514 matching lines @@
         sources = [
           "android/icudtl_dat.S",
         ]
       } else {
         assert(false, "No icu data for this platform")
       }
       defines = [ "U_HIDE_DATA_SYMBOL" ]
     }
   }
 }