Add subsetting to SkScanlineDecoder

src/codec/SkCodecPriv.h

Index: src/codec/SkCodecPriv.h
diff --git a/src/codec/SkCodecPriv.h b/src/codec/SkCodecPriv.h
index 0442625dd20b858ee7e9cd84877f3417124fcbd1..2f1b3c1c0bcf4832308de2ac557c8effab518cdc 100644
--- a/src/codec/SkCodecPriv.h
+++ b/src/codec/SkCodecPriv.h
@@ -31,6 +31,8 @@
 #define COMPUTE_RESULT_ALPHA                    \
     SkSwizzler::GetResult(zeroAlpha, maxAlpha);
 
+inline float get_scale_from_sample_size(uint32_t sampleSize) { return 1.0f / (float) sampleSize; }

[scroggo, 2015/10/08 20:16:07]

This change (moving this function here, removing SkCodecTools, and including
SkCodecPriv where you previously included SkCodecTools) seems like it should be
its own change. It doesn't appear to be newly used by anything else here.

That said, I'm not sure it's the right thing to do. Not sure if dm etc should
rely on src/codec. (I think we do rely on other private includes, so it's at
least no worse than we already do.)

[msarett, 2015/10/09 20:03:44]

I'll remove this from the change.

Right now, get_scale_from_sample_size is used in dm and nanobench.  My thought
process was that anything that is used by more than one of dm, nanobench, tools
should go in SkCodecPriv.h but maybe that is wrong.

+
 /*
  * returns a scaled dimension based on the original dimension and the sampleSize
  * NOTE: we round down here for scaled dimension to match the behavior of SkImageDecoder