Revert of Remove unused (by clients) SkUnitMapper (https://codereview.chromium.org/283273002/) (https://codereview.chromium.org/288343009/)

Reason for revert:
required blink change failed to land

Original issue's description:
> Remove unused (by clients) SkUnitMapper (https://codereview.chromium.org/283273002/)
>
> This reverts commit dd50c83b5b34dab3a077741861b50ed1f2bc6b8f.
>
> BUG=skia:
>
> Committed: http://code.google.com/p/skia/source/detail?r=14830

R=scroggo@google.com, reed@google.com
TBR=reed@google.com, scroggo@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Author: reed@chromium.org

Review URL: https://codereview.chromium.org/296823008

git-svn-id: http://skia.googlecode.com/svn/trunk@14838 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/gradient_matrix.cpp b/gm/gradient_matrix.cpp
index 275acc8..4f2915a 100644
--- a/gm/gradient_matrix.cpp
+++ b/gm/gradient_matrix.cpp
@@ -63,7 +63,7 @@
 
 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, 0, &localMatrix);
+                                          SkShader::kClamp_TileMode, NULL, 0, &localMatrix);
 }
 
 static SkShader* make_radial_gradient(const SkPoint pts[2], const SkMatrix& localMatrix) {
@@ -72,7 +72,7 @@
                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, 0, &localMatrix);
+                                          SkShader::kClamp_TileMode, NULL, 0, &localMatrix);
 }
 
 static void draw_gradients(SkCanvas* canvas,