Sky: Add a DrawLooper interface to the painting API to be used for shadows.

sky/engine/core/painting/DrawLooperAddLayerCallback.h

Index: sky/engine/core/painting/DrawLooperAddLayerCallback.h
diff --git a/sky/engine/core/painting/DrawLooperAddLayerCallback.h b/sky/engine/core/painting/DrawLooperAddLayerCallback.h
new file mode 100644
index 0000000000000000000000000000000000000000..364cdb0d70d4cd6e050a59635f7ff6e714543047
--- /dev/null
+++ b/sky/engine/core/painting/DrawLooperAddLayerCallback.h
@@ -0,0 +1,19 @@
+// 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.
+
+#ifndef SKY_ENGINE_CORE_PAINTING_DRAWLOOPERADDLAYERCALLBACK_H_
+#define SKY_ENGINE_CORE_PAINTING_DRAWLOOPERADDLAYERCALLBACK_H_
+
+namespace blink {
+class Paint;
+
+class DrawLooperAddLayerCallback {
+ public:
+  virtual ~DrawLooperAddLayerCallback();
+  virtual void handleEvent(Paint* context) = 0;
+};
+
+} // namespace blink
+
+#endif  // SKY_ENGINE_CORE_PAINTING_DRAWLOOPERADDLAYERCALLBACK_H_