When a surface is backed by an external render target force a copy on image snap

src/gpu/GrGpuResource.cpp

Index: src/gpu/GrGpuResource.cpp
diff --git a/src/gpu/GrGpuResource.cpp b/src/gpu/GrGpuResource.cpp
index 98cea1c9a8c21ca0480461fc84f977fee7fc3ad2..7c053b31d702e160ddfde601ae3422b2d1fbf5b2 100644
--- a/src/gpu/GrGpuResource.cpp
+++ b/src/gpu/GrGpuResource.cpp
@@ -169,7 +169,7 @@ void GrGpuResource::setScratchKey(const GrScratchKey& scratchKey) {
     SkASSERT(!fScratchKey.isValid());
     SkASSERT(scratchKey.isValid());
     // Wrapped resources can never have a scratch key.
-    if (this->cacheAccess().isExternal()) {
+    if (this->resourcePriv().isExternal()) {
         return;
     }
     fScratchKey = scratchKey;