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

bench/benchmain.cpp

Index: bench/benchmain.cpp
===================================================================
--- bench/benchmain.cpp	(revision 13305)
+++ bench/benchmain.cpp	(working copy)
@@ -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();