[iOS/GN] Fix the compilation of "all" on iOS with gn.

services/shell/standalone/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("//mojo/public/mojo_application.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//testing/test.gni")
 
 executable("standalone") {
   output_name = "mojo_runner"
   sources = [
     "desktop/main.cc",
   ]
   deps = [
     ":lib",
     "//base",
     "//build/config/sanitizers:deps",
     "//build/win:default_exe_manifest",
   ]
 }
 
 source_set("lib") {
   sources = [
-    "context.cc",
-    "context.h",
     "desktop/launcher_process.cc",
     "desktop/launcher_process.h",
     "desktop/main_helper.cc",
     "desktop/main_helper.h",
     "tracer.cc",
     "tracer.h",
   ]
 
   deps = [
     "//base",
     "//base:base_static",
     "//base/third_party/dynamic_annotations",
     "//components/tracing:startup_tracing",
     "//mojo/edk/system",
     "//services/catalog:lib",
     "//services/shell",
     "//services/shell/public/cpp",
     "//services/shell/runner/host:lib",
     "//services/tracing/public/cpp",
     "//services/tracing/public/interfaces",
     "//url",
   ]
 
   data_deps = [
     "//services/tracing",
   ]
 
+  if (!is_ios) {
+    sources += [
+      "context.cc",
+      "context.h",
+    ]
+  }
+
   # This target includes some files behind #ifdef OS... guards. Since gn is not
   # smart enough to understand preprocess includes, it does complains about
   # these includes when not using the build files for that OS. Suppress checking
   # so we can enable checking for the rest of the targets in this file.
   # TODO: Might be better to split the files with OS-specific includes out to a
   # separate source_set so we can leave checking on for the rest of the target.
   check_includes = false
 }