Add support for linear gradients, implemented as skia shaders.

sky/engine/core/painting/Shader.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/core/painting/CanvasPath.h"
+#include "sky/engine/core/painting/Shader.h"
 
 namespace blink {
 
-CanvasPath::CanvasPath()
-{
+Shader::Shader(PassRefPtr<SkShader> shader)
+    : shader_(shader) {
 }
 
-CanvasPath::~CanvasPath()
-{
+Shader::~Shader() {
 }
 
 } // namespace blink