Introduce PaintingContext, which will be used for custom painting

sky/engine/core/painting/Paint.cpp

 // 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.
 
 #include "sky/engine/config.h"
-#include "sky/engine/tonic/dart_class_provider.h"
+#include "sky/engine/core/painting/Paint.h"
 
 namespace blink {
 
-DartClassProvider::~DartClassProvider() {
+Paint::Paint()
+{
 }
 
-}  // namespace blink
+Paint::~Paint()
+{
+}
+
+} // namespace blink