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/tests/PipeTest.cpp b/tests/PipeTest.cpp
index 3b89441..e5d2f09 100644
--- a/tests/PipeTest.cpp
+++ b/tests/PipeTest.cpp
@@ -18,7 +18,7 @@
 #include "SkPictureRecorder.h"
 
 static void drain(SkPipeDeserializer* deserial, SkDynamicMemoryWStream* stream) {
-    std::unique_ptr<SkCanvas> canvas(SkCreateNullCanvas());
+    std::unique_ptr<SkCanvas> canvas = SkMakeNullCanvas();
     sk_sp<SkData> data = stream->detachAsData();
     deserial->playback(data->data(), data->size(), canvas.get());
 }