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

src/core/SkImageFilter.cpp

Index: src/core/SkImageFilter.cpp
diff --git a/src/core/SkImageFilter.cpp b/src/core/SkImageFilter.cpp
index b2c04450fff42d12b112a4316b05fba3b3a528a3..64b62759e2c8b83dfd1ba0d61d161a61008b92bd 100644
--- a/src/core/SkImageFilter.cpp
+++ b/src/core/SkImageFilter.cpp
@@ -22,6 +22,7 @@
 #include "GrContext.h"
 #include "GrDrawContext.h"
 #include "GrFixedClip.h"
+#include "SkGrPriv.h"
 #endif
 
 #ifndef SK_IGNORE_TO_STRING
@@ -282,9 +283,10 @@ sk_sp<SkSpecialImage> SkImageFilter::DrawWithFP(GrContext* context,
     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;