[gn] Port icu_use_data_file_flag in 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("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 # Because standalone V8 builds are not supported, assume this is part of a
 # Chromium build.
 import("//build_overrides/v8.gni")
 
 import("snapshot_toolchain.gni")
 
 declare_args() {
+  # Use ICU data file (icudtl.dat) if true or library (shared on windows,
+  # static otherwise).
+  icu_use_data_file_flag = true
+
   # Enable the snapshot feature, for fast context creation.
   # http://v8project.blogspot.com/2015/09/custom-startup-snapshots.html
   v8_use_snapshot = true
 
   # Use external files for startup data blobs:
   # the JS builtins sources and the start snapshot.
   v8_use_external_startup_data = true
 
   # Sets -DVERIFY_HEAP.
   v8_enable_verify_heap = false
@@ skipping 1798 matching lines @@
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     cflags = [ "/wd4267" ]
   }
 
   if (v8_enable_i18n_support) {
     deps += [ "//third_party/icu" ]
     if (is_win) {
       deps += [ "//third_party/icu:icudata" ]
     }
 
-    # TODO(jochen): Add support for icu_use_data_file_flag
-    defines += [ "ICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE" ]
+    if (icu_use_data_file_flag) {
+      defines += [ "ICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE" ]
+    } else if (is_win) {
+      defines += [ "ICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_SHARED" ]
+    } else {
+      defines += [ "ICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_STATIC" ]
+    }
   } else {
     sources -= [
       "src/i18n.cc",
       "src/i18n.h",
     ]
   }
 
   if (v8_postmortem_support) {
     sources += [ "$target_gen_dir/debug-support.cc" ]
     deps += [ ":postmortem-metadata" ]
@@ skipping 336 matching lines @@
   sources = [
     "test/fuzzer/wasm-asmjs.cc",
   ]
 
   deps = [
     ":fuzzer_support",
   ]
 
   configs = [ ":internal_config" ]
 }