Inline extensions .gypi files into GN build.

extensions/utility/BUILD.gn

Index: extensions/utility/BUILD.gn
diff --git a/extensions/utility/BUILD.gn b/extensions/utility/BUILD.gn
index 9a29a68fd83a8dde91930e9aa704858b7bd11b2d..facc84625be7b2f3e6f4f0876fe80e5104a9c67e 100644
--- a/extensions/utility/BUILD.gn
+++ b/extensions/utility/BUILD.gn
@@ -3,15 +3,16 @@
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
-import("//extensions/extensions.gni")
 
 assert(enable_extensions)
 
-# GYP version: extensions/extensions.gyp:extensions_utility
 source_set("utility") {
-  sources = rebase_path(extensions_gypi_values.extensions_utility_sources,
-                        ".",
-                        "//extensions")
+  sources = [
+    "unpacker.cc",
+    "unpacker.h",
+    "utility_handler.cc",
+    "utility_handler.h",
+  ]
 
   # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]