Introduce PaintingContext, which will be used for custom painting

sky/engine/core/painting/Paint.idl

Index: sky/engine/core/painting/Paint.idl
diff --git a/sky/engine/core/painting/Paint.idl b/sky/engine/core/painting/Paint.idl
new file mode 100644
index 0000000000000000000000000000000000000000..886be59d13a1d557cf5cc773144fca7939cf1c76
--- /dev/null
+++ b/sky/engine/core/painting/Paint.idl
@@ -0,0 +1,12 @@
+// Copyright 2015 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.
+
+[
+  Constructor(),
+] interface Paint {
+  attribute boolean isAntiAlias;
+  attribute unsigned long color;
+
+  void setARGB(unsigned long a, unsigned long r, unsigned long g, unsigned long b);
+};