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

src/core/SkImageFilter.cpp

 /*
  * Copyright 2012 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 "SkImageFilter.h"
 
 #include "SkCanvas.h"
 #include "SkFuzzLogging.h"
 #include "SkImageFilterCache.h"
 #include "SkLocalMatrixImageFilter.h"
 #include "SkMatrixImageFilter.h"
 #include "SkReadBuffer.h"
 #include "SkRect.h"
 #include "SkSpecialImage.h"
 #include "SkSpecialSurface.h"
 #include "SkValidationUtils.h"
 #include "SkWriteBuffer.h"
 #if SK_SUPPORT_GPU
 #include "GrContext.h"
 #include "GrDrawContext.h"
 #include "GrFixedClip.h"
+#include "SkGrPriv.h"
 #endif
 
 #ifndef SK_IGNORE_TO_STRING
 void SkImageFilter::CropRect::toString(SkString* str) const {
     if (!fFlags) {
         return;
     }
 
     str->appendf("cropRect (");
     if (fFlags & CropRect::kHasLeft_CropEdge) {
@@ skipping 240 matching lines @@
 
 #if SK_SUPPORT_GPU
 sk_sp<SkSpecialImage> SkImageFilter::DrawWithFP(GrContext* context,
                                                 sk_sp<GrFragmentProcessor> fp,
                                                 const SkIRect& bounds,
                                                 sk_sp<SkColorSpace> colorSpace) {
     GrPaint paint;
     paint.addColorFragmentProcessor(std::move(fp));
     paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
 
+    GrPixelConfig config = GrRenderableConfigForColorSpace(colorSpace.get());
     sk_sp<GrDrawContext> drawContext(context->makeDrawContext(SkBackingFit::kApprox,
                                                               bounds.width(), bounds.height(),
-                                                              kRGBA_8888_GrPixelConfig,
+                                                              config,
                                                               std::move(colorSpace)));
     if (!drawContext) {
         return nullptr;
     }
 
     SkIRect dstIRect = SkIRect::MakeWH(bounds.width(), bounds.height());
     SkRect srcRect = SkRect::Make(bounds);
     SkRect dstRect = SkRect::MakeWH(srcRect.width(), srcRect.height());
     GrFixedClip clip(dstIRect);
     drawContext->fillRectToRect(clip, paint, SkMatrix::I(), dstRect, srcRect);
@@ skipping 145 matching lines @@
     sk_sp<SkSpecialImage> result(input->filterImage(src, this->mapContext(ctx), offset));
 
     SkASSERT(!result || src->isTextureBacked() == result->isTextureBacked());
 
     return result;
 }
 
 void SkImageFilter::PurgeCache() {
     SkImageFilterCache::Get()->purge();
 }