Move more sources from modules.gypi to subdirectories.

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

Index: third_party/WebKit/Source/modules/csspaint/BUILD.gn
diff --git a/third_party/WebKit/Source/modules/csspaint/BUILD.gn b/third_party/WebKit/Source/modules/csspaint/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..5b9132778698fdfbf1cf1f966a05b15ad321de9b
--- /dev/null
+++ b/third_party/WebKit/Source/modules/csspaint/BUILD.gn
@@ -0,0 +1,23 @@
+# 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("csspaint") {
+  sources = [
+    "CSSPaintDefinition.cpp",
+    "CSSPaintDefinition.h",
+    "CSSPaintImageGeneratorImpl.cpp",
+    "CSSPaintImageGeneratorImpl.h",
+    "PaintRenderingContext2D.cpp",
+    "PaintRenderingContext2D.h",
+    "PaintSize.h",
+    "PaintWorklet.cpp",
+    "PaintWorklet.h",
+    "PaintWorkletGlobalScope.cpp",
+    "PaintWorkletGlobalScope.h",
+    "WindowPaintWorklet.cpp",
+    "WindowPaintWorklet.h",
+  ]
+}