DM: use SkBitmap::reset()

dm/DM.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "CrashHandler.h"
 #include "DMJsonWriter.h"
 #include "DMSrcSink.h"
@@ skipping 475 matching lines @@
     }
 
     // Convert our N32 bitmap into unpremul RGBA for libpng.
     SkAutoTMalloc<uint32_t> rgba(w*h);
     if (!bitmap.readPixels(SkImageInfo::Make(w,h, kRGBA_8888_SkColorType, kUnpremul_SkAlphaType),
                            rgba, 4*w, 0,0)) {
         return false;
     }
 
     // We don't need bitmap anymore.  Might as well drop our ref.
-    bitmap = SkBitmap();
+    bitmap.reset();
 
     FILE* f = fopen(path, "w");
     if (!f) { return false; }
 
     png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
     if (!png) {
         fclose(f);
         return false;
     }
 
@@ skipping 401 matching lines @@
     }
     return 0;
 }
 
 #if !defined(SK_BUILD_FOR_IOS)
 int main(int argc, char** argv) {
     SkCommandLineFlags::Parse(argc, argv);
     return dm_main();
 }
 #endif