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

BUG=skia:
R=scroggo@google.com, dominikg@chromium.org

Author: reed@google.com

Review URL: https://codereview.chromium.org/264843006

git-svn-id: http://skia.googlecode.com/svn/trunk@14514 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/gradients/SkGradientShaderPriv.h b/src/effects/gradients/SkGradientShaderPriv.h
index c1e253f..a699c4c 100644
--- a/src/effects/gradients/SkGradientShaderPriv.h
+++ b/src/effects/gradients/SkGradientShaderPriv.h
@@ -142,9 +142,7 @@
 
     class GradientShaderBaseContext : public SkShader::Context {
     public:
-        GradientShaderBaseContext(const SkGradientShaderBase& shader, const SkBitmap& device,
-                                  const SkPaint& paint, const SkMatrix& matrix);
-        ~GradientShaderBaseContext() {}
+        GradientShaderBaseContext(const SkGradientShaderBase& shader, const ContextRec&);
 
         virtual uint32_t getFlags() const SK_OVERRIDE { return fFlags; }