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

src/gpu/GrDrawingManager.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrDrawingManager.h"
 
 #include "GrContext.h"
@@ skipping 204 matching lines @@
                                                        sk_sp<SkColorSpace> colorSpace,
                                                        const SkSurfaceProps* surfaceProps) {
     if (this->wasAbandoned()) {
         return nullptr;
     }
 
     // SkSurface catches bad color space usage at creation. This check handles anything that slips
     // by, including internal usage. We allow a null color space here, for read/write pixels and
     // other special code paths. If a color space is provided, though, enforce all other rules.
     if (colorSpace && !SkSurface_Gpu::Valid(fContext, rt->config(), colorSpace.get())) {
+        // SRGBTODO: Enable this assert once image filters are propagating color type and space
+//        SkDEBUGFAIL("Invalid config and colorspace combination");
         return nullptr;
     }
 
     bool useDIF = false;
     if (surfaceProps) {
         useDIF = surfaceProps->isUseDeviceIndependentFonts();
     }
 
     if (useDIF && fContext->caps()->shaderCaps()->pathRenderingSupport() &&
         rt->isStencilBufferMultisampled()) {
         GrStencilAttachment* sb = fContext->resourceProvider()->attachStencilAttachment(rt.get());
         if (sb) {
             return sk_sp<GrDrawContext>(new GrPathRenderingDrawContext(
                                                         fContext, this, std::move(rt),
                                                         std::move(colorSpace), surfaceProps,
                                                         fContext->getAuditTrail(), fSingleOwner));
         }
     }
 
     return sk_sp<GrDrawContext>(new GrDrawContext(fContext, this, std::move(rt),
                                                   std::move(colorSpace), surfaceProps,
                                                   fContext->getAuditTrail(),
                                                   fSingleOwner));
 }