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

dm/DMSrcSink.cpp

 #include "DMSrcSink.h"
 #include "SamplePipeControllers.h"
 #include "SkCommonFlags.h"
 #include "SkDocument.h"
 #include "SkMultiPictureDraw.h"
+#include "SkNullCanvas.h"
 #include "SkOSFile.h"
 #include "SkPictureRecorder.h"
 #include "SkRandom.h"
 #include "SkSVGCanvas.h"
 #include "SkStream.h"
 #include "SkXMLWriter.h"
 
 namespace DM {
 
 GMSrc::GMSrc(skiagm::GMRegistry::Factory factory) : fFactory(factory) {}
@@ skipping 109 matching lines @@
 
 SkISize SKPSrc::size() const {
     // This may be unnecessarily large.
     return kSKPViewport.roundOut().size();
 }
 
 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,
                  GrGLStandard api,
                  int samples,
                  bool dfText,
                  bool threaded)
     : fContextType(ct)
     , fGpuAPI(api)
     , fSampleCount(samples)
@@ skipping 258 matching lines @@
             surfaces.unrefAll();
             return "";
         }
         SkISize size() const SK_OVERRIDE { return fSize; }
         Name name() const SK_OVERRIDE { sk_throw(); return ""; }  // No one should be calling this.
     } proxy(fW, fH, pic, src.size());
     return fSink->draw(proxy, bitmap, stream, log);
 }
 
 }  // namespace DM