Add the ability to decode a subset to SkCodec.

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 239 matching lines @@
 
         // Decode all images to the canvas color type
         push_src("image", "codec", new CodecSrc(path, CodecSrc::kNormal_Mode,
                 CodecSrc::kGetFromCanvas_DstColorType, scale));
         push_src("image", "scanline", new CodecSrc(path, CodecSrc::kScanline_Mode,
                 CodecSrc::kGetFromCanvas_DstColorType, scale));
         push_src("image", "scanline_subset", new CodecSrc(path, CodecSrc::kScanline_Subset_Mode,
                 CodecSrc::kGetFromCanvas_DstColorType, scale));
         push_src("image", "stripe", new CodecSrc(path, CodecSrc::kStripe_Mode,
                 CodecSrc::kGetFromCanvas_DstColorType, scale));
+        // Note: The only codec which supports subsets natively is SkWebpCodec, which will never
+        // report kIndex_8 or kGray_8, so there is no need to test kSubset_mode with those color
+        // types specifically requested.
+        push_src("image", "codec_subset", new CodecSrc(path, CodecSrc::kSubset_Mode,
+                CodecSrc::kGetFromCanvas_DstColorType, scale));
     }
 }
 
 static bool codec_supported(const char* ext) {
     // FIXME: Once other versions of SkCodec are available, we can add them to this
     // list (and eventually we can remove this check once they are all supported).
     static const char* const exts[] = {
         "bmp", "gif", "jpg", "jpeg", "png", "ico", "wbmp", "webp",
         "BMP", "GIF", "JPG", "JPEG", "PNG", "ICO", "WBMP", "WEBP",
     };
@@ skipping 556 matching lines @@
     }
     return 0;
 }
 
 #if !defined(SK_BUILD_FOR_IOS)
 int main(int argc, char** argv) {
     SkCommandLineFlags::Parse(argc, argv);
     return dm_main();
 }
 #endif