Introduce GrColorSpaceXform, for gamut conversion on textures

tests/SRGBMipMapTest.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
 #if SK_SUPPORT_GPU
 #include "GrCaps.h"
@@ skipping 128 matching lines @@
     sk_sp<GrDrawContext> l32DrawContext(
         context->drawContext(sk_ref_sp(l32Texture->asRenderTarget()), &l32Props));
     sk_sp<GrDrawContext> s32DrawContext(
         context->drawContext(sk_ref_sp(s32Texture->asRenderTarget()), &s32Props));
 
     SkRect rect = SkRect::MakeWH(SkIntToScalar(rtS), SkIntToScalar(rtS));
     GrNoClip noClip;
     GrPaint paint;
     paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
     GrTextureParams mipMapParams(SkShader::kRepeat_TileMode, GrTextureParams::kMipMap_FilterMode);
-    paint.addColorTextureProcessor(texture, SkMatrix::MakeScale(0.5f), mipMapParams);
+    paint.addColorTextureProcessor(texture, nullptr, SkMatrix::MakeScale(0.5f), mipMapParams);
 
     // 1) Draw texture to S32 surface (should generate/use sRGB mips)
     paint.setGammaCorrect(true);
     s32DrawContext->drawRect(noClip, paint, SkMatrix::I(), rect);
     read_and_check_pixels(reporter, s32Texture, expectedSRGB, error, "first render of sRGB");
 
     // 2) Draw texture to L32 surface (should generate/use linear mips)
     paint.setGammaCorrect(false);
     l32DrawContext->drawRect(noClip, paint, SkMatrix::I(), rect);
     read_and_check_pixels(reporter, l32Texture, expectedLinear, error, "re-render as linear");
 
     // 3) Go back to sRGB
     paint.setGammaCorrect(true);
     s32DrawContext->drawRect(noClip, paint, SkMatrix::I(), rect);
     read_and_check_pixels(reporter, s32Texture, expectedSRGB, error, "re-render as sRGB");
 }
 #endif