Fourth fragment from "Reduce dependence on GrSurface's origin field"

TBR=bsalomon@google.com
Change-Id: I8ed3b1f5e468d99b3ac06e8cfdf74b49042813f8
Reviewed-on: https://skia-review.googlesource.com/26144
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>

src/image/SkImage_Lazy.cpp

@@ -697,6 +697,7 @@ public:
 static void set_key_on_proxy(GrResourceProvider* resourceProvider,
                              GrTextureProxy* proxy, const GrUniqueKey& key) {
     if (key.isValid()) {
+        SkASSERT(proxy->origin() == kTopLeft_GrSurfaceOrigin);
         resourceProvider->assignUniqueKeyToProxy(key, proxy);
     }
 }