Upgrade SkSpecialImage to have getTextureRef & getROPixels entry points

src/core/SkImageFilter.cpp

Index: src/core/SkImageFilter.cpp
diff --git a/src/core/SkImageFilter.cpp b/src/core/SkImageFilter.cpp
index 743dc2ad1afaf08685a27b45c7a609c23fdeb262..fb5c9157b67da79a996cd50b8d7856d4f984ad9d 100644
--- a/src/core/SkImageFilter.cpp
+++ b/src/core/SkImageFilter.cpp
@@ -601,10 +601,10 @@ sk_sp<SkSpecialImage> SkImageFilter::filterInput(int index,
     sk_sp<SkSpecialImage> result(input->filterImage(src, this->mapContext(ctx), offset));
 
 #if SK_SUPPORT_GPU
-    if (src->peekTexture() && result && !result->peekTexture()) {
+    if (src->isTextureBacked() && result && !result->isTextureBacked()) {
         // Keep the result on the GPU - this is still required for some
         // image filters that don't support GPU in all cases
-        GrContext* context = src->peekTexture()->getContext();
+        GrContext* context = src->getContext();
         return result->makeTextureImage(src->internal_getProxy(), context);
     }
 #endif