Fix ref-counting error when reseting a SkiaCanvas with a new SkCanvas.

Change-Id: Id2ed6627674cbd3112d6ac80f4e29a5ff65606b6
diff --git a/libs/hwui/SkiaCanvas.cpp b/libs/hwui/SkiaCanvas.cpp
index db4e857..99ea831 100644
--- a/libs/hwui/SkiaCanvas.cpp
+++ b/libs/hwui/SkiaCanvas.cpp
@@ -45,7 +45,7 @@
 }
 
 void SkiaCanvas::reset(SkCanvas* skiaCanvas) {
-    mCanvas.reset(skiaCanvas);
+    mCanvas.reset(SkRef(skiaCanvas));
     mSaveStack.reset(nullptr);
     mHighContrastText = false;
 }