Add support for linear gradients, implemented as skia shaders.

sky/engine/core/painting/Shader.cpp

Index: sky/engine/core/painting/Shader.cpp
diff --git a/sky/engine/core/painting/CanvasPath.cpp b/sky/engine/core/painting/Shader.cpp
similarity index 64%
copy from sky/engine/core/painting/CanvasPath.cpp
copy to sky/engine/core/painting/Shader.cpp
index 145ce801363a2baa7f2fc6e05a58f29f6870f122..332dc24504141ab4e398a0596099d69f2a3e2402 100644
--- a/sky/engine/core/painting/CanvasPath.cpp
+++ b/sky/engine/core/painting/Shader.cpp
@@ -3,16 +3,15 @@
 // 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