Fix colorType/alphaType checks in SkCodec

src/codec/SkCodec.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 "SkBmpCodec.h"
 #include "SkCodec.h"
 #include "SkCodecPriv.h"
@@ skipping 148 matching lines @@
             return kInvalidParameters;
         }
     } else {
         if (ctableCount) {
             *ctableCount = 0;
         }
         ctableCount = nullptr;
         ctable = nullptr;
     }
 
-    {
-        SkAlphaType canonical;
-        if (!SkColorTypeValidateAlphaType(info.colorType(), info.alphaType(), &canonical)

[scroggo, 2016/02/12 17:13:55]

What is this redundant with? I started to remove this recently, but convinced
myself we still wanted it.

[msarett, 2016/02/12 17:41:31]

This just checks that the alphaType matches the colorType.

So we return kInvalidConversion if k565 or kGray is not matched with kOpaque.  I
think that if conversion_possible handles this check, then we don't need it
here.

If we want to handle it here, startScanlineDecode() is missing this check.

[scroggo, 2016/02/12 17:59:00]

Ah, got it. So you're just moving this into a common place where it's called by
startScanlineDecode.

It might be nice to leave it here (and include it for scanline decoding), so
when this gets updated codec gets updated for free. I don't feel strongly about
that though.

-            || canonical != info.alphaType())
-        {
-            return kInvalidConversion;
-        }
-    }
-
     if (!this->rewindIfNeeded()) {
         return kCouldNotRewind;
     }
 
     // Default options.
     Options optsStorage;
     if (nullptr == options) {
         options = &optsStorage;
     } else if (options->fSubset) {
         SkIRect subset(*options->fSubset);
@@ skipping 186 matching lines @@
             SkASSERT(1 == linesRequested || this->getInfo().height() == linesRequested);
             const SkImageInfo fillInfo = info.makeWH(info.width(), 1);
             for (int srcY = linesDecoded; srcY < linesRequested; srcY++) {
                 fillDst = SkTAddOffset<void>(dst, this->outputScanline(srcY) * rowBytes);
                 fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);
             }
             break;
         }
     }
 }