Refactor how WebCrypto NSS and OpenSSL specific files are included by GN build.

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/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//content/child/child.gni")
 
 source_set("child") {
@@ skipping 89 matching lines @@
   if (use_aura && is_mac) {
     # This file is already excluded on non-Mac.
     sources -= [ "npapi/webplugin_delegate_impl_mac.mm" ]
   }
 
   if (is_win || !use_aura) {
     sources -= [ "npapi/webplugin_delegate_impl_aura.cc" ]
   }
 
   if (!use_openssl) {
-    sources -= [ "webcrypto/platform_crypto_openssl.cc" ]
+    sources += rebase_path(content_child_gypi_values.webcrypto_nss_sources,
+                           ".", "//content")
   } else {
-    sources -= [ "webcrypto/platform_crypto_nss.cc" ]
+    sources += rebase_path(content_child_gypi_values.webcrypto_openssl_sources,
+                           ".", "//content")
   }
 }