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

src/effects/SkXfermodeImageFilter.cpp

 /*
  * Copyright 2013 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkXfermodeImageFilter.h"
 
 #include "SkCanvas.h"
 #include "SkColorPriv.h"
 #include "SkReadBuffer.h"
 #include "SkSpecialImage.h"
 #include "SkSpecialSurface.h"
 #include "SkWriteBuffer.h"
 #include "SkXfermode.h"
 #if SK_SUPPORT_GPU
 #include "GrContext.h"
 #include "GrDrawContext.h"
 #include "effects/GrConstColorProcessor.h"
 #include "effects/GrTextureDomain.h"
 #include "effects/GrSimpleTextureEffect.h"
 #include "SkGr.h"
+#include "SkGrPriv.h"
 #endif
 
 ///////////////////////////////////////////////////////////////////////////////
 
 sk_sp<SkImageFilter> SkXfermodeImageFilter::Make(sk_sp<SkXfermode> mode,
                                                  sk_sp<SkImageFilter> background,
                                                  sk_sp<SkImageFilter> foreground,
                                                  const CropRect* cropRect) {
     sk_sp<SkImageFilter> inputs[2] = { std::move(background), std::move(foreground) };
     return sk_sp<SkImageFilter>(new SkXfermodeImageFilter(mode, inputs, cropRect));
@@ skipping 199 matching lines @@
         // A null 'xferFP' here means kSrc_Mode was used in which case we can just proceed
         if (xferFP) {
             paint.addColorFragmentProcessor(std::move(xferFP));
         }
     } else {
         paint.addColorFragmentProcessor(std::move(bgFP));
     }
 
     paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
 
-    sk_sp<GrDrawContext> drawContext(context->makeDrawContext(SkBackingFit::kApprox,
-                                                              bounds.width(), bounds.height(),
-                                                              kSkia8888_GrPixelConfig,
-                                                              sk_ref_sp(source->getColorSpace())));
+    sk_sp<GrDrawContext> drawContext(
+        context->makeDrawContext(SkBackingFit::kApprox, bounds.width(), bounds.height(),
+                                 GrRenderableConfigForColorSpace(source->getColorSpace()),
+                                 sk_ref_sp(source->getColorSpace())));
     if (!drawContext) {
         return nullptr;
     }
     paint.setAllowSRGBInputs(drawContext->isGammaCorrect());
 
     SkMatrix matrix;
     matrix.setTranslate(SkIntToScalar(-bounds.left()), SkIntToScalar(-bounds.top()));
     drawContext->drawRect(GrNoClip(), paint, matrix, SkRect::Make(bounds));
 
     return SkSpecialImage::MakeFromGpu(SkIRect::MakeWH(bounds.width(), bounds.height()),
                                        kNeedNewImageUniqueID_SpecialImage,
                                        drawContext->asTexture(),
                                        sk_ref_sp(drawContext->getColorSpace()));
 }
 
 #endif