Towards removing getTexture() on SkImage

Review URL: https://codereview.chromium.org/1166993002
diff --git a/src/gpu/SkGpuDevice.cpp b/src/gpu/SkGpuDevice.cpp
index edb887c..6db5c1d 100644
--- a/src/gpu/SkGpuDevice.cpp
+++ b/src/gpu/SkGpuDevice.cpp
@@ -1474,7 +1474,7 @@
 }
 
 static bool wrap_as_bm(const SkImage* image, SkBitmap* bm) {
-    GrTexture* tex = image->getTexture();
+    GrTexture* tex = as_IB(image)->getTexture();
     if (tex) {
         GrWrapTextureInBitmap(tex, image->width(), image->height(), image->isOpaque(), bm);
         return true;