remove unused (by clients) SkUnitMapper

gm/gradient_matrix.cpp

Index: gm/gradient_matrix.cpp
diff --git a/gm/gradient_matrix.cpp b/gm/gradient_matrix.cpp
index 4f2915ab4dab43b68cb431869b5635f4e013ef27..275acc88684cd22e3dd30750e33b8e61a97007e8 100644
--- a/gm/gradient_matrix.cpp
+++ b/gm/gradient_matrix.cpp
@@ -63,7 +63,7 @@ static const int IMAGES_X = 4;             // number of images per row
 
 static SkShader* make_linear_gradient(const SkPoint pts[2], const SkMatrix& localMatrix) {
     return SkGradientShader::CreateLinear(pts, gColors, NULL, SK_ARRAY_COUNT(gColors),
-                                          SkShader::kClamp_TileMode, NULL, 0, &localMatrix);
+                                          SkShader::kClamp_TileMode, 0, &localMatrix);
 }
 
 static SkShader* make_radial_gradient(const SkPoint pts[2], const SkMatrix& localMatrix) {
@@ -72,7 +72,7 @@ static SkShader* make_radial_gradient(const SkPoint pts[2], const SkMatrix& loca
                SkScalarAve(pts[0].fY, pts[1].fY));
     float radius = (center - pts[0]).length();
     return SkGradientShader::CreateRadial(center, radius, gColors, NULL, SK_ARRAY_COUNT(gColors),
-                                          SkShader::kClamp_TileMode, NULL, 0, &localMatrix);
+                                          SkShader::kClamp_TileMode, 0, &localMatrix);
 }
 
 static void draw_gradients(SkCanvas* canvas,