DM: remove unnecessary use of std::function

dm/DMSrcSink.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "DMSrcSink.h"
 #include "SkAndroidCodec.h"
 #include "SkCodec.h"
@@ skipping 1025 matching lines @@
     SkCanvas canvas(*dst);
     return src.draw(&canvas);
 }
 
 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
 
 // Handy for front-patching a Src.  Do whatever up-front work you need, then call draw_to_canvas(),
 // passing the Sink draw() arguments, a size, and a function draws into an SkCanvas.
 // Several examples below.
 
+template <typename Fn>
 static Error draw_to_canvas(Sink* sink, SkBitmap* bitmap, SkWStream* stream, SkString* log,
-                            SkISize size, std::function<Error(SkCanvas*)> draw) {
+                            SkISize size, const Fn& draw) {
     class ProxySrc : public Src {
     public:
-        ProxySrc(SkISize size, std::function<Error(SkCanvas*)> draw) : fSize(size), fDraw(draw) {}
+        ProxySrc(SkISize size, const Fn& draw) : fSize(size), fDraw(draw) {}
         Error   draw(SkCanvas* canvas) const override { return fDraw(canvas); }
         Name                    name() const override { sk_throw(); return ""; } // Won't be called.
         SkISize                 size() const override { return fSize; }
     private:
-        SkISize                         fSize;
-        std::function<Error(SkCanvas*)> fDraw;
+        SkISize   fSize;
+        const Fn& fDraw;
     };
     return sink->draw(ProxySrc(size, draw), bitmap, stream, log);
 }
 
 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
 
 DEFINE_bool(check, true, "If true, have most Via- modes fail if they affect the output.");
 
 // Is *bitmap identical to what you get drawing src into sink?
 static Error check_against_reference(const SkBitmap* bitmap, const Src& src, Sink* sink) {
@@ skipping 339 matching lines @@
             skr.visit<void>(i, drawsAsSingletonPictures);
         }
         SkAutoTUnref<SkPicture> macroPic(macroRec.endRecordingAsPicture());
 
         canvas->drawPicture(macroPic);
         return check_against_reference(bitmap, src, fSink);
     });
 }
 
 }  // namespace DM