Introduce the Background Fetch module.

third_party/WebKit/Source/modules/background_fetch/BUILD.gn

Index: third_party/WebKit/Source/modules/background_fetch/BUILD.gn
diff --git a/third_party/WebKit/Source/modules/background_fetch/BUILD.gn b/third_party/WebKit/Source/modules/background_fetch/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..33d44004b817cb1b2d8a9039886929547291cf3d
--- /dev/null
+++ b/third_party/WebKit/Source/modules/background_fetch/BUILD.gn
@@ -0,0 +1,14 @@
+# Copyright 2017 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("//third_party/WebKit/Source/modules/modules.gni")
+
+blink_modules_sources("background_fetch") {
+  sources = [
+    "BackgroundFetchManager.cpp",
+    "BackgroundFetchManager.h",
+    "ServiceWorkerRegistrationBackgroundFetch.cpp",
+    "ServiceWorkerRegistrationBackgroundFetch.h",
+  ]
+}