Revert[2] "Change SkCanvas to *not* inherit from SkRefCnt"

Changes over original:
- conditionalize ownership in SkPictureRecorder
- conditionalize ownership in SkCanvasStateUtils

This reverts commit b613c266df48cf45296ecc23d1bd7098c84bb7ba.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4742

Change-Id: Ib25514d6f546c69b6650b5c957403b04f7380dc2
Reviewed-on: https://skia-review.googlesource.com/4742
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/tools/skp_parser.cpp b/tools/skp_parser.cpp
index d242524..887c50d 100644
--- a/tools/skp_parser.cpp
+++ b/tools/skp_parser.cpp
@@ -34,7 +34,7 @@
     SkISize size = pic->cullRect().roundOut().size();
     SkDebugCanvas debugCanvas(size.width(), size.height());
     pic->playback(&debugCanvas);
-    sk_sp<SkCanvas> nullCanvas(SkCreateNullCanvas());
+    std::unique_ptr<SkCanvas> nullCanvas = SkMakeNullCanvas();
     UrlDataManager dataManager(SkString("data"));
     Json::Value json = debugCanvas.toJSON(
             dataManager, debugCanvas.getSize(), nullCanvas.get());