Test scanline decoding in DM.

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 72 matching lines @@
 
     Error draw(SkCanvas*) const SK_OVERRIDE;
     SkISize size() const SK_OVERRIDE;
     Name name() const SK_OVERRIDE;
 private:
     skiagm::GMRegistry::Factory fFactory;
 };
 
 class CodecSrc : public Src {
 public:
-    explicit CodecSrc(Path path);
+    enum Mode {
+        kNormal_Mode,
+        kScanline_Mode,
+    };
+    CodecSrc(Path, Mode);
 
     Error draw(SkCanvas*) const SK_OVERRIDE;
     SkISize size() const SK_OVERRIDE;
     Name name() const SK_OVERRIDE;
 private:
     Path fPath;
+    Mode fMode;
 };
 
 
 class ImageSrc : public Src {
 public:
     // divisor == 0 means decode the whole image
     // divisor > 0 means decode in subsets, dividing into a divisor x divisor grid.
     explicit ImageSrc(Path path, int divisor = 0);
 
     Error draw(SkCanvas*) const SK_OVERRIDE;
@@ skipping 147 matching lines @@
     const char* fileExtension() const SK_OVERRIDE { return fSink->fileExtension(); }
 private:
     const int                   fW, fH;
     SkAutoTDelete<SkBBHFactory> fFactory;
     SkAutoTDelete<Sink>         fSink;
 };
 
 }  // namespace DM
 
 #endif//DMSrcSink_DEFINED