color: general transformation -> affine transformation

ui/gfx/color_transform.h

 // Copyright (c) 2016 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_COLOR_TRANSFORM_H_
 #define UI_GFX_COLOR_TRANSFORM_H_
 
 #include <memory>
 #include <stdint.h>
 
 #include "build/build_config.h"
 #include "ui/gfx/geometry/point3_f.h"
 #include "ui/gfx/gfx_export.h"
+#include "ui/gfx/transform.h"
 
 namespace gfx {
 
 class ColorSpace;
 
 class GFX_EXPORT ColorTransform {
  public:
   enum class Intent { INTENT_ABSOLUTE, INTENT_PERCEPTUAL };
 
   // TriStimulus is a color coordinate in any color space.
   // Channel order is XYZ, RGB or YUV.
   typedef Point3F TriStim;
 
   virtual ~ColorTransform() {}
 
   // Perform transformation of colors, |colors| is both input and output.
-  virtual void transform(TriStim* colors, size_t num) = 0;
+  virtual void transform(TriStim* colors, size_t num) const = 0;
+
+  // Create an affine approximation of this transform. No guarantees
+  // are made as to how accurate the approximation is.
+  // Returns true if successful, false if there was a failure.
+  // This operation can be somewhat costly, considering caching the result
+  // if you plan to use this frequently.
+  virtual bool GetAffineApproximation(Transform* transform) const;
 
   static std::unique_ptr<ColorTransform> NewColorTransform(
       const ColorSpace& from,
       const ColorSpace& to,
       Intent intent);
 };
 }  // namespace gfx
 
 #endif  // UI_GFX_COLOR_TRANSFORM_H_