Fix crash in bench when "--mode record" is used

R=mtklein@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/150633008

git-svn-id: http://skia.googlecode.com/svn/trunk@13310 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/bench/benchmain.cpp b/bench/benchmain.cpp
index 2d88626..49ef00d 100644
--- a/bench/benchmain.cpp
+++ b/bench/benchmain.cpp
@@ -603,7 +603,7 @@
 
                 if ((benchMode == kRecord_BenchMode || benchMode == kPictureRecord_BenchMode)) {
                     // Clear the recorded commands so that they do not accumulate.
-                    canvas.reset(recordTo.beginRecording(dim.fX, dim.fY, kRecordFlags));
+                    canvas.reset(SkRef(recordTo.beginRecording(dim.fX, dim.fY, kRecordFlags)));
                 }
 
                 timer.start();