Move more sources from modules.gypi to subdirectories.

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

Index: third_party/WebKit/Source/modules/app_banner/BUILD.gn
diff --git a/third_party/WebKit/Source/modules/app_banner/BUILD.gn b/third_party/WebKit/Source/modules/app_banner/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..7ba856a906b57285dd2740319b53af2e0af048c8
--- /dev/null
+++ b/third_party/WebKit/Source/modules/app_banner/BUILD.gn
@@ -0,0 +1,18 @@
+# Copyright 2016 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("app_banner") {
+  sources = [
+    "AppBannerCallbacks.cpp",
+    "AppBannerCallbacks.h",
+    "AppBannerController.cpp",
+    "AppBannerController.h",
+    "AppBannerPromptResult.cpp",
+    "AppBannerPromptResult.h",
+    "BeforeInstallPromptEvent.cpp",
+    "BeforeInstallPromptEvent.h",
+  ]
+}