Temporary fix for --preAbandonGpuContext bug

src/core/SkSpecialImage.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file
  */
 #include "SkSpecialImage.h"
 
 #if SK_SUPPORT_GPU
 #include "GrTexture.h"
@@ skipping 463 matching lines @@
         if (!fTexture->readPixels(0, 0, result->width(), result->height(), kSkia8888_GrPixelConfig,
                                   result->getPixels(), result->rowBytes())) {
             return false;
         }
 
         result->pixelRef()->setImmutable();
         return true;
     }
 
     sk_sp<SkSpecialSurface> onMakeSurface(const SkImageInfo& info) const override {
+        if (!fTexture->getContext()) {
+            return nullptr;
+        }
+
         GrSurfaceDesc desc = GrImageInfoToSurfaceDesc(info, *fTexture->getContext()->caps());
         desc.fFlags = kRenderTarget_GrSurfaceFlag;
 
         return SkSpecialSurface::MakeRenderTarget(this->proxy(), fTexture->getContext(), desc);
     }
 
     sk_sp<SkSpecialImage> onMakeSubset(const SkIRect& subset) const override {
         return SkSpecialImage::MakeFromGpu(this->internal_getProxy(),
                                            subset,
                                            this->uniqueID(),
@@ skipping 50 matching lines @@
 
 sk_sp<SkSpecialImage> SkSpecialImage::MakeFromGpu(SkImageFilter::Proxy* proxy,
                                                   const SkIRect& subset,
                                                   uint32_t uniqueID,
                                                   GrTexture* tex,
                                                   SkAlphaType at) {
     return nullptr;
 }
 
 #endif