Add a Via to DM that records into two pictures and draws using the second.

dm/DMSrcSink.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef DMSrcSink_DEFINED
 #define DMSrcSink_DEFINED
 
@@ skipping 248 matching lines @@
 
     Error draw(const Src&, SkBitmap*, SkWStream*, SkString*) const override;
     int enclave() const override { return fSink->enclave(); }
     const char* fileExtension() const override { return fSink->fileExtension(); }
 private:
     const int                   fW, fH;
     SkAutoTDelete<SkBBHFactory> fFactory;
     SkAutoTDelete<Sink>         fSink;
 };
 
+class ViaSecondPicture : public Sink {
+public:
+    explicit ViaSecondPicture(Sink*);
+
+    Error draw(const Src&, SkBitmap*, SkWStream*, SkString*) const override;
+    int enclave() const override { return fSink->enclave(); }
+    const char* fileExtension() const override { return fSink->fileExtension(); }
+private:
+    SkAutoTDelete<Sink>  fSink;
+};
+
 }  // namespace DM
 
 #endif//DMSrcSink_DEFINED