Add CodecZeroInit test to DMSrcSink

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 82 matching lines @@
 
     Error draw(SkCanvas*) const override;
     SkISize size() const override;
     Name name() const override;
     void modifyGrContextOptions(GrContextOptions* options) const override;
 
 private:
     skiagm::GMRegistry::Factory fFactory;
 };
 
 class CodecSrc : public Src {

[msarett, 2016/01/12 15:02:33]

I think you could make the argument that fZeroInit should be a bool field on
CodecSrc (and AndroidCodecSrc and BRDSrc), so that we test all of the modes on
zero init memory.

However, I don't think we want to double the time it takes to test.  The
interesting code to test is the swizzle functions, which will be exercised by
SkCodec::getPixels().

[scroggo, 2016/01/12 22:27:46]

sgtm. Maybe add a comment explaining that in the code along with the enum?

[msarett, 2016/01/13 14:58:16]

Done.

 public:
     enum Mode {
         kCodec_Mode,
+        kCodecZeroInit_Mode,
         kScanline_Mode,
         kStripe_Mode, // Tests the skipping of scanlines
         kSubset_Mode, // For codecs that support subsets directly.
     };
     enum DstColorType {
         kGetFromCanvas_DstColorType,
         kIndex8_Always_DstColorType,
         kGrayscale_Always_DstColorType,
     };
     CodecSrc(Path, Mode, DstColorType, float);
@@ skipping 241 matching lines @@
 
 class ViaTwice : public Via {
 public:
     explicit ViaTwice(Sink* sink) : Via(sink) {}
     Error draw(const Src&, SkBitmap*, SkWStream*, SkString*) const override;
 };
 
 }  // namespace DM
 
 #endif//DMSrcSink_DEFINED