Add gypi_to_gn for content/utility sources list

content/content_utility.gypi

Index: content/content_utility.gypi
diff --git a/content/content_utility.gypi b/content/content_utility.gypi
index b202787c8f8088fd02b115629f836116bdf1e7db..bbdfd4fe27443e1ddc63d07282f5d667cfc6aa0e 100644
--- a/content/content_utility.gypi
+++ b/content/content_utility.gypi
@@ -7,22 +7,30 @@
     '../base/base.gyp:base',
     '../courgette/courgette.gyp:courgette_lib',
   ],
-  'sources': [
-    'public/utility/content_utility_client.cc',
-    'public/utility/content_utility_client.h',
-    'public/utility/utility_thread.cc',
-    'public/utility/utility_thread.h',
-    'utility/in_process_utility_thread.cc',
-    'utility/in_process_utility_thread.h',
-    'utility/utility_blink_platform_impl.cc',
-    'utility/utility_blink_platform_impl.h',
-    'utility/utility_main.cc',
-    'utility/utility_thread_impl.cc',
-    'utility/utility_thread_impl.h',
-    'utility/webthread_impl_for_utility_thread.cc',
-    'utility/webthread_impl_for_utility_thread.h',
-  ],
+  'variables': {
+    'utility_sources': [
+      'utility/in_process_utility_thread.cc',
+      'utility/in_process_utility_thread.h',
+      'utility/utility_blink_platform_impl.cc',
+      'utility/utility_blink_platform_impl.h',
+      'utility/utility_main.cc',
+      'utility/utility_thread_impl.cc',
+      'utility/utility_thread_impl.h',
+      'utility/webthread_impl_for_utility_thread.cc',
+      'utility/webthread_impl_for_utility_thread.h',
+    ],
+    'public_utility_sources': [
+      'public/utility/content_utility_client.cc',
+      'public/utility/content_utility_client.h',
+      'public/utility/utility_thread.cc',
+      'public/utility/utility_thread.h',
+    ],
+  },
   'include_dirs': [
     '..',
   ],
+  'sources': [
+    '<@(public_utility_sources)',
+    '<@(utility_sources)',
+  ],
 }