Move ScopedIPCSupport into its own build rule.

content/child/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/features.gni")
 import("//build/config/ui.gni")
 import("//content/child/child.gni")
 
 source_set("child") {
   # Targets external to content should always link to the public API.
@@ skipping 30 matching lines @@
     "//components/tracing",
     "//components/tracing:startup_tracing",
     "//components/webcrypto",
     "//content/app/resources",
     "//content/app/strings",
     "//content/common",
     "//content/public/common:common_sources",
     "//crypto:platform",
     "//gpu/command_buffer/client",
     "//ipc/mojo",
+    "//ipc/mojo:ipc_support",
     "//media",
     "//mojo/common",
     "//mojo/edk/system",
     "//net",
     "//services/shell/public/interfaces",
     "//services/shell/runner/common",
     "//skia",
     "//storage/common",
     "//third_party/WebKit/public:blink_headers",
     "//third_party/WebKit/public:image_resources",
@@ skipping 39 matching lines @@
 
 # See comment at the top of //content/BUILD.gn for how this works.
 group("for_content_tests") {
   visibility = [ "//content/test/*" ]
   if (!is_component_build) {
     public_deps = [
       ":child",
     ]
   }
 }