Add color space support to 4f gradients

Similar to the raster pipeline stage, transform the stops into the dest
color space before interpolation.

Change-Id: I626b6ef18606fd2308d7da166ce70d05f3951e21
Reviewed-on: https://skia-review.googlesource.com/18767
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/src/shaders/gradients/SkGradientShaderPriv.h b/src/shaders/gradients/SkGradientShaderPriv.h
index 7a66eda..c7c7761 100644
--- a/src/shaders/gradients/SkGradientShaderPriv.h
+++ b/src/shaders/gradients/SkGradientShaderPriv.h
@@ -202,6 +202,8 @@
 
     uint32_t getGradFlags() const { return fGradFlags; }
 
+    SkColor4f getXformedColor(size_t index, SkColorSpace*) const;
+
 protected:
     struct Rec {
         SkFixed     fPos;   // 0...1