Add scaled subset API to SkCodec

src/codec/SkSwizzler.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
 #include "SkScaledCodec.h"
@@ skipping 692 matching lines @@
     , fBPP(bpp)
     , fSampleX(1)
 {}
 
 int SkSwizzler::onSetSampleX(int sampleX) {
     SkASSERT(sampleX > 0); // Surely there is an upper limit? Should there be
                            // way to report failure?
     fSampleX = sampleX;
     fX0 = get_start_coord(sampleX) + fSrcOffset;
     fDstWidth = get_scaled_dimension(fSrcWidth, sampleX);
-

[msarett, 2015/10/12 18:33:29]

I missed this in an earlier CL, but this check is no longer valid.

We may want a ten pixel subset that starts twenty pixels from the left edge of
the image.

This is completely valid, but in this case fX0 = 20 and fSrcWidth = 10.

[scroggo, 2015/10/12 20:47:07]

Wait, does this belong in crrev.com/1390213002? I would prefer it go in with
that one (or by itself) than here.

-    // check that fX0 is less than original width
-    SkASSERT(fX0 >= 0 && fX0 < fSrcWidth);
     return fDstWidth;
 }
 
 SkSwizzler::ResultAlpha SkSwizzler::swizzle(void* dst, const uint8_t* SK_RESTRICT src) {
     SkASSERT(nullptr != dst && nullptr != src);
     return fRowProc(dst, src, fDstWidth, fBPP, fSampleX * fBPP, fX0 * fBPP, fColorTable);
 }