Add LinearBoxGradient and RadialBoxGradient decorations for RenderDecoratedBox.

sky/engine/core/painting/CanvasGradient.cpp

Index: sky/engine/core/painting/CanvasGradient.cpp
diff --git a/sky/engine/core/painting/CanvasGradient.cpp b/sky/engine/core/painting/CanvasGradient.cpp
index d8286faa7be0b0b2652bae4b36aedcd4b04d8821..8f287693197f49da9e457627515617cb80f07033 100644
--- a/sky/engine/core/painting/CanvasGradient.cpp
+++ b/sky/engine/core/painting/CanvasGradient.cpp
@@ -21,7 +21,6 @@ void CanvasGradient::initLinear(const Vector<Point>& end_points,
   for (int i = 0; i < 2; ++i)
     sk_end_points[i] = end_points[i].sk_point;
 
-  // TODO(mpcomplete): allow setting the TileMode.
   SkShader* shader = SkGradientShader::CreateLinear(
       sk_end_points, colors.data(), color_stops.data(), colors.size(),
       tile_mode);