Support decoding opaque images to unpremul/premul

tests/CodexTest.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 "Resources.h"
 #include "SkBitmap.h"
 #include "SkCodec.h"
@@ skipping 94 matching lines @@
 
     SkMD5::Digest digest;
     md5(bm, &digest);
 
     // verify that re-decoding gives the same result.
     test_info(r, codec, info, SkCodec::kSuccess, &digest);
 
     {
         // Check alpha type conversions
         if (info.alphaType() == kOpaque_SkAlphaType) {
+            // Decoding to either premul or unpremul should succeed and look no different
+            test_info(r, codec, info.makeAlphaType(kUnpremul_SkAlphaType), SkCodec::kSuccess,
+                      &digest);
+            test_info(r, codec, info.makeAlphaType(kPremul_SkAlphaType), SkCodec::kSuccess,
+                      &digest);
         } else {
             // Decoding to opaque should fail
             test_info(r, codec, info.makeAlphaType(kOpaque_SkAlphaType),
                       SkCodec::kInvalidConversion, NULL);
             SkAlphaType otherAt = info.alphaType();
             if (kPremul_SkAlphaType == otherAt) {
                 otherAt = kUnpremul_SkAlphaType;
             } else {
                 otherAt = kPremul_SkAlphaType;
             }
@@ skipping 226 matching lines @@
     REPORTER_ASSERT(r, SkCodec::kInvalidParameters == result);
     result = decoder->start(
         decoder->getInfo().makeColorType(kIndex_8_SkColorType));
     REPORTER_ASSERT(r, SkCodec::kInvalidParameters == result);
 }
 
 DEF_TEST(Codec_Params, r) {
     test_invalid_parameters(r, "index8.png");
     test_invalid_parameters(r, "mandrill.wbmp");
 }