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/drawbitmaprect.cpp b/gm/drawbitmaprect.cpp
index 33a13f0..d9b1434 100644
--- a/gm/drawbitmaprect.cpp
+++ b/gm/drawbitmaprect.cpp
@@ -63,7 +63,7 @@
                         colors, pos,
                         SK_ARRAY_COUNT(colors),
                         SkShader::kRepeat_TileMode,
-                        0, &mat))->unref();
+                        NULL, 0, &mat))->unref();
         canvas.drawRect(rect, paint);
         rect.inset(wScalar / 8, hScalar / 8);
         mat.postScale(SK_Scalar1 / 4, SK_Scalar1 / 4);