Correct sRGB <-> linear everywhere.

src/core/SkLinearBitmapPipeline_sample.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkLinearBitmapPipeline_sampler_DEFINED
 #define SkLinearBitmapPipeline_sampler_DEFINED
 
@@ skipping 152 matching lines @@
     Sk4f*                fColorTable;
 };
 
 template <SkGammaType gammaType>
 class PixelConverter<kGray_8_SkColorType, gammaType> {
 public:
     using Element = uint8_t;
     PixelConverter(const SkPixmap& srcPixmap) { }
 
     Sk4f toSk4f(Element pixel) const {
-        float gray = pixel * (1.0f/255.0f);
-        Sk4f result = Sk4f{gray, gray, gray, 1.0f};
-        return gammaType == kSRGB_SkGammaType
-               ? srgb_to_linear(result)
-               : result;
+        float gray = (gammaType == kSRGB_SkGammaType)
+            ? sk_linear_from_srgb[pixel]
+            : pixel * (1/255.0f);
+        return {gray, gray, gray, 1.0f};
     }
 };
 
 template <>
 class PixelConverter<kRGBA_F16_SkColorType, kLinear_SkGammaType> {
 public:
     using Element = uint64_t;
     PixelConverter(const SkPixmap& srcPixmap) { }
 
     Sk4f toSk4f(const Element pixel) const {
@@ skipping 637 matching lines @@
         }
     }
 
     Next* const fNext;
     Accessor    fAccessor;
 };
 
 }  // namespace
 
 #endif  // SkLinearBitmapPipeline_sampler_DEFINED