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

ios/crnet/crnet_consumer/BUILD.gn

+# Copyright 2016 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/ios/rules.gni")
+
+ios_app_bundle("crnet_consumer") {
+  info_plist = "crnet-consumer-info.plist"
+
+  deps = [
+    "//base",
+    "//ios/crnet:crnet_framework+link",
+    "//ios/crnet:crnet_sources",
+
+    # All shared libraries must have the sanitizer deps to properly link in
+    # asan mode (this target will be empty in other cases).
+    "//build/config/sanitizers:deps",
+  ]
+
+  sources = [
+    "crnet_consumer_app_delegate.h",
+    "crnet_consumer_app_delegate.mm",
+    "crnet_consumer_view_controller.h",
+    "crnet_consumer_view_controller.m",
+    "main.mm",
+  ]
+
+  bundle_deps = [ "//ios/crnet:crnet_framework+bundle" ]
+
+  configs += [ "//build/config/compiler:enable_arc" ]
+}