Fix some GPU image filter code to preserve precision and color space

src/gpu/SkGrPriv.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkGrPriv_DEFINED
 #define SkGrPriv_DEFINED
 
@@ skipping 87 matching lines @@
                                  sk_sp<GrFragmentProcessor> fp,
                                  bool textureIsAlphaOnly,
                                  GrPaint* grPaint);
 
 //////////////////////////////////////////////////////////////////////////////
 
 GrSurfaceDesc GrImageInfoToSurfaceDesc(const SkImageInfo&, const GrCaps&);
 
 bool GrPixelConfigToColorType(GrPixelConfig, SkColorType*);
 
+/** When image filter code needs to construct a draw context to do intermediate rendering, we need
+    a renderable pixel config. The source (SkSpecialImage) may not be in a renderable format, but
+    we want to preserve the color space of that source. This picks an appropriate format to use. */

[robertphillips, 2016/09/21 13:44:10]

Should this take a const SkColorSpace* ?

+GrPixelConfig GrRenderableConfigForColorSpace(SkColorSpace*);
+
 /**
  *  If the compressed data in the SkData is supported (as a texture format, this returns
  *  the pixel-config that should be used, and sets outStartOfDataToUpload to the ptr into
  *  the data where the actual raw data starts (skipping any header bytes).
  *
  *  If the compressed data is not supported, this returns kUnknown_GrPixelConfig, and
  *  ignores outStartOfDataToUpload.
  */
 GrPixelConfig GrIsCompressedTextureDataSupported(GrContext* ctx, SkData* data,
                                                  int expectedW, int expectedH,
@@ skipping 30 matching lines @@
 GR_STATIC_ASSERT((int)kIDC_GrBlendCoeff == (int)SkXfermode::kIDC_Coeff);
 GR_STATIC_ASSERT((int)kSA_GrBlendCoeff == (int)SkXfermode::kSA_Coeff);
 GR_STATIC_ASSERT((int)kISA_GrBlendCoeff == (int)SkXfermode::kISA_Coeff);
 GR_STATIC_ASSERT((int)kDA_GrBlendCoeff == (int)SkXfermode::kDA_Coeff);
 GR_STATIC_ASSERT((int)kIDA_GrBlendCoeff == (int)SkXfermode::kIDA_Coeff);
 GR_STATIC_ASSERT(SkXfermode::kCoeffCount == 10);
 
 #define SkXfermodeCoeffToGrBlendCoeff(X) ((GrBlendCoeff)(X))
 
 #endif