DM: don't leak the null canvas in NullSink.

dm/DMSrcSink.cpp

Index: dm/DMSrcSink.cpp
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index b0df70b12488b0ecfceb8e8c6220a3dd3414a82a..4e3668f15e5545a5192adb58d9f0538516aa9218 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -3,6 +3,7 @@
 #include "SkCommonFlags.h"
 #include "SkDocument.h"
 #include "SkMultiPictureDraw.h"
+#include "SkNullCanvas.h"
 #include "SkOSFile.h"
 #include "SkPictureRecorder.h"
 #include "SkRandom.h"
@@ -132,6 +133,13 @@ Name SKPSrc::name() const { return SkOSPath::Basename(fPath.c_str()); }
 
 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
 
+Error NullSink::draw(const Src& src, SkBitmap*, SkWStream*, SkString*) const {
+    SkAutoTDelete<SkCanvas> canvas(SkCreateNullCanvas());
+    return src.draw(canvas);
+}
+
+/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+
 DEFINE_bool(gpuStats, false, "Append GPU stats to the log for each GPU task?");
 
 GPUSink::GPUSink(GrContextFactory::GLContextType ct,