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

Reason for revert:
does not address all legacy callsites in chrome.

e.g.

[13:45:32.091872] ../../ui/native_theme/native_theme_base.cc:608:76: error: no matching function for call to ‘SkGradientShader::CreateLinear(SkPoint [3], SkColor [3], NULL, int, SkShader::TileMode, NULL)’
[13:45:32.091919]            gradient_bounds, colors, NULL, 3, SkShader::kClamp_TileMode, NULL));


Original issue's description:
> remove unused (by clients) SkUnitMapper
>
> BUG=skia:
>
> Committed: http://code.google.com/p/skia/source/detail?r=14761

R=robertphillips@google.com, scroggo@google.com, george@mozilla.com
TBR=george@mozilla.com, robertphillips@google.com, scroggo@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Author: reed@google.com

Review URL: https://codereview.chromium.org/287063009

git-svn-id: http://skia.googlecode.com/svn/trunk@14763 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/alphagradients.cpp b/gm/alphagradients.cpp
index d108288..e63fbc9 100644
--- a/gm/alphagradients.cpp
+++ b/gm/alphagradients.cpp
@@ -29,7 +29,8 @@
         SkPaint paint;
         uint32_t flags = doPreMul ? SkGradientShader::kInterpolateColorsInPremul_Flag : 0;
         SkShader* s = SkGradientShader::CreateLinear(pts, colors, NULL, 2,
-                                                     SkShader::kClamp_TileMode, flags, NULL);
+                                                     SkShader::kClamp_TileMode,
+                                                     NULL, flags);
         paint.setShader(s)->unref();
         canvas->drawRect(r, paint);