Add UMAs for numerical approximation of table-based transfer functions.

ui/gfx/skia_color_space_util.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_SKIA_COLOR_SPACE_UTIL_H_
 #define UI_GFX_SKIA_COLOR_SPACE_UTIL_H_
 
 #include "third_party/skia/include/core/SkColorSpace.h"
 #include "ui/gfx/gfx_export.h"
 
 namespace gfx {
 
 float GFX_EXPORT SkTransferFnEval(const SkColorSpaceTransferFn& fn, float x);
 
 SkColorSpaceTransferFn GFX_EXPORT
 SkTransferFnInverse(const SkColorSpaceTransferFn& fn);
 
 bool GFX_EXPORT
 SkTransferFnsApproximatelyCancel(const SkColorSpaceTransferFn& a,
                                  const SkColorSpaceTransferFn& b);
 
 bool GFX_EXPORT
 SkTransferFnIsApproximatelyIdentity(const SkColorSpaceTransferFn& fn);
 
+void GFX_EXPORT SkApproximateTransferFn(const float* x,
+                                        const float* t,
+                                        size_t n,
+                                        SkColorSpaceTransferFn* fn,
+                                        float* error,
+                                        bool* nonlinear_fit_converged);
+
 bool GFX_EXPORT SkMatrixIsApproximatelyIdentity(const SkMatrix44& m);
 
 }  // namespace gfx
 
 #endif  // UI_GFX_SKIA_COLOR_SPACE_UTIL_H_