create struct to hold all the params passed around for shader::context

src/effects/gradients/SkGradientShader.cpp

Index: src/effects/gradients/SkGradientShader.cpp
diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 6d753a9508d8c9b1d11ab5bcb0164d5e1ed4907a..d376b2223696d45569d8389dda073ec90e3f1921 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -253,9 +253,8 @@ bool SkGradientShaderBase::isOpaque() const {
 }
 
 SkGradientShaderBase::GradientShaderBaseContext::GradientShaderBaseContext(
-        const SkGradientShaderBase& shader, const SkBitmap& device,
-        const SkPaint& paint, const SkMatrix& matrix)
-    : INHERITED(shader, device, paint, matrix)
+        const SkGradientShaderBase& shader, const ContextRec& rec)
+    : INHERITED(shader, rec)
     , fCache(shader.refCache(getPaintAlpha()))
 {
     const SkMatrix& inverse = this->getTotalInverse();